Donald Trump promised the American people he would build a “big, beautiful wall” along the US-Mexico border. At campaign rallies, it became a call and response. In a lot of ways, it became a joke. To some, it became a taunt at high school basketball games, a way to make clear some kinds of people aren’t welcome here. Most of all, the wall was easily the most identifiable campaign promise of any candidate in the 2016 election cycle — maybe of any candidate in a generation.

Now that Trump is president, that promise is coming due.

The Trump administration now wants to see the wall built. They are absolutely serious about it. Even though it lost the first round of the funding battle in Congress, when legislators refused to give the administration billions of dollars over the summer, it’s requesting $1.6 billion in wall funding in the 2018 budget. And the Department of Homeland Security is reviewing proposals to build prototypes — 30-foot-long segments at least 18 feet high — somewhere around San Diego.

How far the wall goes from symbol to reality is anyone’s guess. There are a ton of obstacles in the way: physical, legal, financial, operational. And at every step, the Trump administration will have to plot a path between the symbolic fantasy of the wall and the small, mundane, human realities of the people living on the border.

1) Why do we need a wall?

Before he was elected, Trump liked to say that the US practically “doesn’t have a border.” Unsurprisingly, he was not exactly telling the truth.

According to the Government Accountability Office, there are 651.7 miles of fencing along the US-Mexico border. The first fencing was built in the 1990s, along the westernmost sector of the border (known as the San Diego Sector). But the current fencing regime is largely the product of the 2006 Secure Fence Act, which passed with overwhelming bipartisan support (backed by then-Sen. Hillary Clinton and Sen. Chuck Schumer) and which required 650 miles of fencing along certain areas of the border.

There’s some evidence that fencing has been effective — or, at least, that it’s been part of a broader strategy of bulking up border security that’s been effective.

The government estimates how many people are crossing the US-Mexico border by looking at how many are caught — and by that measure, the flow of unauthorized people into the US in 2016 was one-quarter of what it was in 2000.

In the San Diego sector, in particular — where the border cuts through an urban area and it might be easy for people to slip by unnoticed — stepped-up enforcement in the 1990s led to more apprehensions at first (as more people got caught), and then fewer apprehensions as people stopped trying.

The question is whether it’s enough.

Securing the border has historically been a policy argument, about what types of fencing are most effective, most cost-effective, and most helpful to Border Patrol agents.

Even before Trump, there was a years-long legislative debate about whether it’s the right kind of fencing. It hasn’t been an argument about politics or symbolism. Until now.

The Secure Fence Act originally specified double-layer fencing, which is more expensive to build but also much harder to cut and cross through. Today, a fraction of the 650 miles of fencing count as “double layer.”

Less than half of the existing fencing is thick enough to prevent pedestrians from crossing (the rest is “vehicle fencing” that can’t be driven through but can be navigated on foot). And even “pedestrian fencing” isn’t always effective: The lowest apprehension rate along the entire US-Mexico border, where only an estimated 17 percent of border crossers are caught, is the sections of the El Paso sector that are “completely covered” by pedestrian fencing built in the past 10 years.

When George W. Bush’s Department of Homeland Security said that double fencing wasn’t feasible for large swaths of the southern border, the Secure Fence Act was amended in 2007 to give the government more authority to determine what counted as a sufficient fence. To many Republicans, though, that seemed like a cop-out, and they’ve spent years accusing the government of not having finished the job right.

Regardless of how wildly inaccurate Donald Trump was about the state of border security, a lot of people believe he’s correct — including the core supporters who made him a force to be reckoned with in the 2016 Republican presidential primary. Those voters are either unaware that there’s currently a fence or simply don’t believe a fence is enough. They want something absolutely foolproof and impregnable, or at least a symbol against attack.

The Trump administration is already struggling to reconcile its wild promises of a “big, beautiful wall” with the existing policy reality. When DHS asked for wall prototypes, it initially specified that the wall had to be concrete, which would have been extremely unlikely to fly with Border Patrol agents, who prefer something they can see through — then hastily added a separate request for non-concrete “alternative” materials.

White House press secretary Sean Spicer bragged that the funding bill passed by Congress in May will allow the government to build fencing — and got into an argument with a Breitbart reporter during a press briefing when the reporter pointed out those fences weren’t a wall.

Building a concrete wall — something that no one within government has asked for — would be more symbolic than practical. But simply building more fencing, and calling it a “wall,” would be, in a significant way, cheating.

2) How realistic is it to build one continuous wall across the border?

Not even a little bit.

As Sen. Heidi Heitkamp (D-ND) said during a Senate hearing on border security, “There has been no one that has come before this body suggesting that we need to build a concrete wall across the border — no one. Not one person, no matter what political persuasion.”

Selling the wall in Congress will be tough, in other words. But that’s nothing compared to the practical realities of trying to actually build it.

For one thing, you have the Rio Grande, which defines the easternmost 1,164 miles of the border. There’s some fencing (if only a little) in each of the four border “sectors” along the Rio Grande; much of it is set back from the river, forcing people to turn back after entering US territory instead of preventing their entry to begin with.

It’s not enough to prevent people from crossing — more than half of all unauthorized entries from 2013 to 2015 happened in the four easternmost Border Patrol sectors, all of which are entirely on the Rio Grande. But it makes fencing construction tricky.

But the real problem is the canyons.

“If you look out in Big Bend,” says Chris Cabrera, deputy spokesperson for the National Border Patrol Council, the union representing US Border Patrol agents, “you have huge drop-offs, huge cliffs. It would be very difficult to build a wall over there, especially when you’re looking at about a 40-, 50-foot drop from ground level to the river.”

Cabrera — and everyone else — sees border security as a three-pronged effort: infrastructure, which includes barriers to keep people from crossing; surveillance, to inform agents when people are crossing; and personnel, to catch people trying to cross.

There’s no magic ratio of the three that makes for ideal security; given the astounding variety of terrain along the border, and the variety of uses to which humans have put its land, what’s most needed depends on where it’s going to be placed.

The wall, Cabrera hopes, will “funnel them, or slow them down, into areas where we can apprehend them a little easier”

Barriers are most important “where you have a city that’s right up against the border,” explains National Border Patrol Council spokesperson Shawn Moran. Smuggling organizations tend to have “infrastructure and support” in urban areas — and people crossing on their own have an easy time blending into the crowd.

Cabrera says that in the Rio Grande Valley, “we have areas where it’s a less than 10-second run from the river to an urban area, where it’s built up and they can hide. That’s a very difficult place to patrol because of the timing; you have to be right on top of it when they cross.”

This is why the San Diego area was the first part of the border to get fenced, and why fencing has been most effective there and (to a lesser extent) in El Paso.

Using fencing strategically means not putting it places where it won’t be effective — but instead pushing people toward unfenced parts of the border that are either harder to cross or easier to patrol. Agents call this “funneling”; the wall, Cabrera hopes, will “funnel them, or slow them down, into areas where we can apprehend them a little easier.”

At Big Bend, for example, the same cliffs that make building a wall so daunting give agents a huge advantage on patrol. “When you have a 40-, 50-foot cliff,” Cabrera says, “you can rest assured it’s going to be difficult to scale that thing unnoticed.” When fences started going up in California, immigrants turned to the Arizona desert instead — which was harder to cross unmolested because it was simply harder to cross. It was deadlier (hundreds of immigrants died every year), but it made those who survived easier to spot and catch.

Funneling isn’t a foolproof strategy. People can still cross in fenced areas, and no one thinks you can design a perfect enough funneling system that agents will catch everyone coming through the funnel’s mouth. To people like Cabrera and Moran, the point of building a wall (however it’s defined) is to improve on the existing funneling, and make it as effective as possible. But to people who are looking for something rock solid and symbolic, that might not help either.

3) What about a virtual wall?

The easy — or at least seemingly easy — way to get around the question of when a barrier counts as a wall: define a wall as something else entirely.

Some Republicans in Congress, like Lindsey Graham, are already doing this: saying the wall will be built but it will be a “virtual wall,” based on surveillance rather than physical prevention.

This might sound innovative. It’s not. It’s something the government has been trying to do for decades.

Before Republicans tried to pivot to a “virtual wall,” the Bush and Obama administrations tried to pivot from the Secure Fence Act to a “virtual fence.” Over the past two decades, there have been no fewer than four separate government initiatives to fix the border using surveillance technology — from a sensors-and-cameras initiative in 1998 to Obama-era experiments with surveillance drones.

“They couldn’t manage to do it right because they were in such a hurry”

All four initiatives were either totally abandoned or quietly considered failures. Very expensive failures.

The problem is that the government has never bothered to lay out, in advance, what goals the new technology was supposed to meet — and how, exactly, it would fit in with the infrastructure and personnel in a realistic border security strategy.

The biggest effort — the SBInet program — was launched in 2006 to use technology to create a “virtual fence.” SBInet was supposed to cover 387 miles of the US border by the end of 2008.

“They couldn’t manage to do it right,” analyst Tom Barry of the TransBorder Project told Homeland Security Newswire in 2010, “because they were in such a hurry to show the American public that the government was fulfilling its responsibility to secure the border and they didn’t do the adequate preparation.”

DHS never bothered to complete a program evaluation to determine how SBInet would contribute to the broader goal of securing the border. Nor did it oversee contractors to prevent cost overruns and delays — or even, one Government Accountability Office audit found, make sure contractors had completed early steps before moving on to later ones.

By 2011, when it was formally canceled, SBInet had been deployed across 53 miles — not quite 14 percent of the area it was supposed to cover. It had cost more than $1 billion.

One might hope that after the SBInet debacle, the Department of Homeland Security has learned its lesson about more careful contractor oversight. But it doesn’t appear to have learned its lesson about asking how a project fits into an actual strategy before moving forward with construction based on “dreams, hopes and fantasy,” as Barry described SBInet.

In other words, the Trump administration can’t use the “virtual wall” label to solve its fundamental dilemma: Should it make incremental improvements based on realistic goals, or do something symbolic and sweeping?

4) How much will the wall cost?

The real answer is nobody knows exactly — mostly because there isn’t a concrete idea of what the “wall” will actually look like.

What’s become increasingly clear is that whatever the wall is, it will be expensive.

Estimates so far have put the price tag anywhere from a low of $12 billion, which was floated by the Trump administration, to $15 billion estimated by House and Senate Leadership to even $21.6 billion, the highest estimated cost in a proposal seen by the Department of Homeland Security — which would be about half DHS’s yearly budget. A recent report put together by Democrats on the Senate Committee on Homeland Security and Governmental Affairs estimated an even higher price tag for the wall and patrolling technology, at a whopping $70 billion — more than four times Trump’s initial figure.

The Democrats’ figure isn’t that unrealistic, either. At the time the Secure Fence Act was passed, Congress estimated the whole project would cost roughly $50 billion over the course of 25 years, which makes Trump’s estimates look especially low, given the fights he is going to have on the ground — particularly in South Texas.

So far, the Trump administration’s supplemental budget request to Congress, requesting $3 billion to begin building the wall, hire border and Immigration and Customs Enforcement agents, and expand detention and deportation programs, failed to make it into the 2017 spending bill. The Democrats successfully blocked all wall funding in the government shutdown negotiations — at least until September.

But wall construction still isn’t at a total standstill. Funding for pending government contracts for wall prototypes is untouched — those contracts were funded through the 2016 budget. Paying for a preliminary model of the wall would likely give more clarity to how much the actual wall would cost.

Trump has turned his eye toward the 2018 budget proposal, which has an additional $2.6 billion for wall construction. To be clear, this would still only be a fraction of the border wall’s estimated cost. And there is a good chance construction will run up the bill once on the ground.

Take McAllen, Texas, a border town on the Rio Grande whose mayor, Jim Darling, has been advocating for levees instead of a wall — an ask city leaders along the more than 1,000 miles of river have made since the Secure Fence Act’s passage. The idea is that levees would help mitigate flooding and provide added security. But prioritizing these demands would be much more expensive than building a typical barrier in Yuma, Arizona, as David Aguilar, a former deputy commissioner of US Customs and Border Protection, admitted in a Senate hearing on the wall.

“You have to decide where you are going to put your resources,” said David Danelo, a national security expert with the Foreign Policy Research Center who has traveled the border extensively. “It’s going to be ugly. There’s going to be cost overruns when it comes to South Texas.”

5) Will Mexico “pay for” the wall?

The other thing that everyone knows about Trump’s wall is that he will “make Mexico pay for it.” That promise seems even more unrealistic than the wall itself.

The Trump administration’s current plan appears to say Trump never promised he’d make Mexico pay for the wall before it was built and to steam ahead, presumably figuring out how to get Mexico to pay at a later date.

The Mexican government certainly won’t write out an oversize charity-style check to the Trump administration for billions of dollars to pay for the wall. But there are a couple of policies the US could push to raise revenue on the backs of Mexico — or Mexicans, or Mexican Americans.

The most prominent idea floated on this front is the border adjustment tax. The proposal would tax Mexican imports and exempt exports (Vox’s Dylan Matthews explains this in greater detail), which counts as raising money because the US currently imports more than it exports. If that remained the case, the revenue raised would far outstrip the cost of the wall. The idea is well-liked by leading House Republicans like Speaker Paul Ryan and Rep. Kevin Brady, who chairs the House’s tax-focused Ways and Means Committee.

But the border adjustment tax was not included in Trump’s one-page tax reform blueprint to Congress. And confusingly, Trump has both said he is interested in a “border adjustment” tax and rejected the idea of what a “border adjustment” tax actually is. Members of the House Freedom Caucus — the conservative faction of the party that successfully moved the Republican health care plan to the right — have already expressed a lot of skepticism about the idea.

“You are adding a whole new tax and revenue stream on the economy and not getting rid of another one — that is always dangerous because it is just one more tax that could go up over time,” Rep. Jim Jordan (R-OH), a founding member of the Freedom Caucus, said. “From a purely philosophical standpoint, I think this is problematic.”

Other solutions floated by Trump during the presidential campaign could be even more aggressive — like taxing remittances sent by people in the US to Mexico, or even confiscating them (a move of extremely dubious legality).

All of these proposals assume that the US is in a position of strength with Mexico — that it holds all the cards and Mexico will be willing (or forced) to go along with whatever decision it makes. But if the Trump administration moves forward on building a wall, talking payment will be the least of its problems with Mexico — and it’s going to find the country less, not more, willing to go along with anything else America wants.

Arturo Sarukhán, former Mexican ambassador to the US, points out that “Mexico and the US ... have been working hand in hand since 9/11” to protect the border from terrorism and crime. “Post-9/11, we understood that if there was a perception that a terrorist threat had materialized across the border in Mexico, the trade relationship that we had been building since 1993, when NAFTA was approved, would collapse.”

Much of the border security efforts over the past 20 years — especially when it comes to the organized criminal networks that would theoretically become a bigger problem once the wall is built — has been done with the cooperation of the Mexican government. In some cases, that’s been undermined by corruption, but often the Mexican government has been successful in intercepting problems before they become the US’s problems.

Mexico, for example, has taken an active role in intercepting Central American children and families journeying to the US — “at a very steep domestic and moral cost for Mexico, because this issue is criticized profoundly across Mexican society,” Sarukhán points out. Mexico shares flight manifests for all flights in Mexican airspace with the US, so that it can catch anyone on the US’s terrorism watch list. American law enforcement agents are allowed to conduct operations on Mexican soil.

Building a wall would be hard to interpret as anything other than a slap in the face to everything Mexico has done for the US over the past 20 years — “the meaning of this is really to separate Mexico,” says Rafael Fernández de Castro, who served in the government of former Mexican President Felipe Calderón. And it might, Sarukhán says, cause Mexico to review — and possibly reconsider — some of its support for the US’s security needs.

“If the wall becomes an issue which contaminates the bilateral agenda as a whole, then it can start having an impact on lots of other things,” says Sarukhán. The wall isn’t supposed to impede trade flows — $1.4 billion in goods flow between the two countries, legally, through ports of entry — but, as Fernández points out, its symbolism undermines Mexico’s decision “to embrace the United States as an economic partner and to try to create a North American economic community” with NAFTA.

“Over the past two decades,” Sarukhán says, the Mexican public “slowly jettisoned its anti-Americanism, and its historical suspicion of the relationship with the US. You’re seeing some of that creeping back into the fabric of Mexican society. You’ve seen some significant calls to boycott US companies, US products, US brands.” And the election of Trump has often been cited as a reason why the left-populist Andrés Manuel López Obrador — who’s promised to take a more antagonistic stance toward the US — is leading in presidential polls.

6) But what about the private property along the US-Mexico border?

Say Trump gets the money, and he somehow figures out a way to build a wall through rivers, canyons, and jungles. He still will have a big problem on his hands: American landowners.

To build the wall, federal officials will have to take a sizable chunk of private land on the southern border away from American citizens, many of whom have owned rights to the land for centuries. Make no mistake, this process would be incredibly time-consuming and expensive for the federal government, and a point of contention with American voters.

“This is a battle,” Rep. Henry Cuellar (D-TX), whose district covers 280 miles of the border, told the Los Angeles Times. “In Texas, we have a long tradition of private property rights. Any time big government starts using eminent domain and taking land — especially the valuable part, access to water — then it becomes a battle cry. Lawsuits will definitely be coming in.”

Take Mauricio Vidaurri, one of Cuellar’s constituents, whose family has owned 1,300 acres of land just 20 miles south of Laredo, Texas, since 1750. Vidaurri is a rancher and an inspector with Customs and Border Protection, and his land extends to the river, where Trump’s wall would be built.

He has some practical concerns; he relies on the water from the river to grow hay on his ranch. Would the wall cut him off from his water source?

Then there’s sentiment. The wall could cut off his family’s nearly 200-year-old cemetery, where his great-grandfather, grandfather, and father, a World War II veteran, are buried. Vidaurri’s situation poses what will likely be one of the biggest challenges for the Trump administration on the road ahead.

The federal government has the legal power to take private land through eminent domain, if it compensates the landowners for the property. But landowners also have the right to due process, which in the past has tied up the government in courts for years.

This has happened before. After the Secure Fence Act’s passage, officials began the long process of buying off people’s lands, and hundreds of landowners fought back. There are still more than 90 cases tied up in court a decade later, according to Terence Garrett, a border security expert with the University of Texas Rio Grande. So far, the government has spent nearly $80 million to compensate landowners to build the existing fencing. The Chicago Tribune reported that Customs and Border Protection “estimates that it will spend an additional $21 million in real estate expenses associated with the remaining condemnation cases, not including about $4 million in Justice Department litigation costs.”

Garrett was personally involved in one of these fights in 2007, when the University of Texas Rio Grande successfully stopped the federal government from building an 18-foot border fence through campus. Instead, it built a 10-foot fence separating campus from a next-door golf course. Another golf course nearby was able to stop building altogether, Garrett said, adding that working-class neighborhoods were notably less successful in winning eminent domain cases. Some offered sentimental and emotional appeals — like the university’s case that the wall would disrupt the bicultural, binational standing of the university. Others have said it would be bad for business.

Put simply, government taking American citizens’ private land is not a popular idea — especially in Texas, where most of these battles will go down. Garrett predicts private landowners will be even more driven to fight against Trump’s wall.

“The difference between this time and last time is that people know what happened last time,” he said.

In California and Arizona, the government already has the rights to most of the border land. But Arizona is also home to the sovereign territory of the Tohono O’odham Nation reservation, which has already come out against building the wall. If the government attempts to build the wall through the 75 miles of sovereign territory in Arizona, it won’t be anything short of a fight.

“You would fundamentally have to change treaty arrangements with them,” said Roger McManus, who is on the board of directors of the Friends of the Sonoran Desert National Monument, a nonprofit that works with federal agencies to protect the natural and cultural resources in Arizona and California. “You would see something that would surpass the [Dakota Access] pipeline situation.”

Then there are the environmental concerns. As Vox’s Eliza Barclay and Sarah Frostenson reported, “the 654 miles of walls and fences already on the US-Mexico border have made a mess out of the environment there.”

With fencing, Border Patrol has made some accommodations for migrating animals in the area — but depending on what this wall would look like, that might no longer be a workaround.

7) Would building the wall even work?

Somehow, as “Build the wall!” became a way to taunt liberal college students and Latino basketball players, the idea of the wall as an actual policy got lost. Would the wall actually stop people from coming over the border without papers?

“We can’t fool ourselves,” says former CBP Deputy Commissioner David Aguilar. “Is there something that is going to guarantee 100 percent that we’re going to seal the border? No, absolutely not.”

It will never be impossible for someone who wants to enter the US to do so if they have the time, resources, and determination. The purpose of border security is to set that bar as high as possible — which means some people will be more easily deterred than others.

Some will simply go under, over, or even through the wall. The best advantage a wall has over a fence is that it’s harder to cut through; the Trump administration’s contract request requires wall prototypes to be able to resist 30 to 90 minutes of drilling with hand tools. But the parts of the border where fencing is most effective (the San Diego area) are also the ones where the government has discovered the most, and most sophisticated, tunnels.

In 2012, DHS reported that it had discovered 140 tunnels over the past two decades — increasing from about five or six per year before 2008 to nearly 10 per year afterward. Many of those tunnels were described as “sophisticated” systems with interlocking passageways and sometimes even lighting and flooring.

The San Diego fence didn’t necessarily cause smugglers to build tunnels instead, but it certainly wasn’t enough to prevent their construction. Furthermore, the very reason fencing is considered so helpful in San Diego — its urban density — made it easy for smugglers to build tunnels without detection: “The buildings on both sides of the border allow for the concealment of tunnel entry and exit points.”

Meanwhile, there’s the threat of drug smuggling drones being piloted across the border. Less futuristic, but more common, is the use of ultralight aircraft to smuggle drug loads over the heads of Border Patrol agents (a trend that’s been simmering for several years). And even if a wall could stretch from sea to shining sea, committed smugglers and immigrants could get into boats or submarines.

The wall is more likely to block some kinds of illegal entries than others

Or smugglers could just continue to do what many of them are doing anyway: cross the border “the right way” — at a port of entry — with contraband in tow.

Customs and Border Protection doesn’t make an effort to estimate how many drugs successfully enter the US — a spokesperson told Vox, “We can’t track what we don’t catch.” But no one believes that agents are catching all the drugs (or people) that smugglers bring into the country through ports of entry, in specially outfitted trucks or thanks to bribing patrol agents. The Drug Enforcement Administration’s 2016 drug threat report says that Mexican drug smuggling organizations, in particular, prefer to send their product into the US through ports — and that hard drugs are particularly likely to be flown into the US, smuggled in on commercial flights.

This doesn’t mean that a wall does nothing. It means the wall is more likely to block some kinds of illegal entries than others. Individuals trying to come to the United States for work or family might successfully be deterred from crossing; cartels aiming to make millions of dollars in cocaine revenue probably will not.

If Border Patrol agents are being freed up to track down and investigate these “sophisticated” criminal enterprises, because they no longer have to round up small groups of immigrants straggling through the desert, that could be one way to define success.

Chris Cabrera of the National Border Patrol Council says this is a strategy smugglers use now to distract border agents: “They know that Border Patrol agents are going to have to come in and apprehend these folks, sometimes 80 to 90 at a time, which is gonna deplete our lines, deplete our resources in the field. And once we pull out of other areas, they can bring across drugs or more high-value human cargo.” A wall would have something like the opposite effect: reducing the distractions of “low-value” immigrant targets and freeing up agents to catch higher-level criminal activity.

There is some evidence that previous border security buildups have succeeded in deterring such “low-value” targets from coming to the US over the past decade (though some scholars argue that the Great Recession played a bigger role). There’s even more evidence that it’s deterred people who were caught once from trying to cross a second time. But it’s not clear whether that’s an indication that the US could be even more effective with even more enforcement, or that the government has already picked the low-hanging fruit.

All things considered, there simply aren’t a lot of “low-value” immigrant targets still coming across the border. Certainly not compared with how many there were in 2000, or even in 2012. The people still coming to the US without papers are, increasingly, children and families from Central America trying to seek asylum — something that, legally speaking, they’re supposed to be able to do by presenting themselves at ports of entry. If the wall is built, they’re supposed to be able to meet someone at the door.

The most unrealistic expectation one could have of the wall is that it could reduce the number of unauthorized immigrants living in the US. Most of the immigrants who are here have been in the US for more than a decade. If anything, the border security buildup back in the 1990s encouraged them to settle in the US and send for family members.

Building a wall now wouldn’t have the same sort of unintended consequences — for the simple reason that it’s already happened. People have already settled. The existing barriers have already changed the border from a place where people can cross back and forth to one that people, at risk of their lives, hope to have to try to cross only once.

Whether you see further enforcement as a worthwhile endeavor depends pretty strongly on whether you see deterring unauthorized migration, in any form — and to any extent — as an important and good thing. If you think of unauthorized immigrants as collateral damage in a war on crime — and see human smuggling, for example, as the inevitable impact of making it harder to get to the US — the effect of a wall on criminal organizations won’t be enough to justify the effect on immigrants’ lives.

But if you think of unauthorized immigration as something that strengthens criminal activity — either because you think “illegal immigrants” are themselves inherently criminal or because you think the demand for human smuggling is driving the supply of smugglers — disrupting immigrants for the sake of hypothetically, slightly, temporarily disrupting criminal organizations is a win-win.

The question then is whether the effect it’s likely to have on disrupting unauthorized migration will be worth the money (and everything else) it costs to build it.

8) Why is it so important for Trump to build the wall?

The wall is Trump’s most identifiable campaign promise. Of course, not all of his voters thought he would literally build a wall to keep that promise — some didn’t even want him to. Polls both before and after the election show that a border wall isn’t a terribly popular idea, even among some Republicans.

One poll conducted by the Pew Research Center, in particular, shows that Republicans living within 350 miles of the US-Mexico border — the people closest to the putative wall — were the least likely to support it.

But this isn’t about Trump’s voters. It’s about his base.

Research indicates that many Americans — particularly white Americans, and particularly a strain of white conservative Americans especially concerned about immigration — are worried about immigration less as a legal issue than as a cultural threat, especially when it comes to Latino immigrants (whom they associate with a different way of life and also, often, with crime). Furthermore, those Americans tend to conflate “illegal immigrants” with “immigrants” and “immigrants” with “Latinos” — leading them to overstate the number of unauthorized immigrants in the country, and imagine more pouring in.

“The average person, particularly if they don’t live anywhere near the US-Mexico border, is probably not going to be able to make a judgment on how threatening the border is based on their own personal experience. What they tend to do is rely on statements made by sources of political information,” says Christopher Federico of the University of Minnesota. Trump told them the border was lawless. Furthermore, he emphasized “in-group/out-group” distinctions like native-born Americans versus immigrants — and “with that usually comes a consciousness of threat.”

President Trump stirred up that threat. He may be able to calm it back down.

In a study published in 2016, researchers asked subjects how much of a threat they felt from Mexican immigration — and then had one group of subjects read an article that emphasized the security that already existed on the US-Mexico border, while another group read one emphasizing the border’s permeability.

Subjects who already felt threatened by Mexican migration and read about the weakness of the border were more likely to overestimate how close Mexico City was to the United States, and to overestimate the number of Mexican immigrants currently living in the US. But people who had felt threatened by Mexican immigration and then read about how strong the border was were likely to feel that Mexico City was further away from the US — and that the Mexican immigrant population was smaller — than it actually was.

You could conclude that the wall will help people threatened by immigration feel safer. Or you could conclude that how safe people feel the border is depends on whether they’re told the border is safe or not.

If Trump wanted to declare victory on border security — with or without a wall — he might be able to persuade many of his supporters that immigration from the south was no longer a threat.

“Trump might say, ‘Okay, we have built a wall, we have fixed this problem, it’s getting better,’” Federico says. “If he very consistently sends a signal like that, and he’s backed by other people in his party in saying the same thing, then I think you would expect to find that among Donald Trump supporters — and the public and Republicans more generally — they might think, ‘Okay, the problem’s getting better. We don’t have to worry about this to the same extent that we used to.’”

He might not even need to build the wall first. The simple fact of having a Republican in office, Federico conjectures, might allow Republicans to worry a little less about border security — in the same way that partisans assume the economy is better when the president is a member of their party. But if Trump actively sent that message, it would be much more effective.

Already the Trump administration is trumpeting a drop in border apprehensions as a victory for the president’s agenda — before a single brick (or transparent-but-still-impenetrable brick equivalent) has been laid.

But not every conservative is going along. Breitbart is pushing Trump officials on building a wall; Rush Limbaugh has already hinted he thinks the administration is caving on it. If that happens, Trump’s base won’t be getting a unified signal that the threat is over. What Trump thinks counts as a “wall” might, ultimately, be less important than what the Breitbart editorial board thinks.

9) Are the costs going to be worth it?

The people who know better than anyone the costs we might pay for a wall are the people who live on the border.

“Those of us (who) have lived along the border have long understood that dealing with Washington’s berrinches (tantrums) is just part of the deal,” former Ambassador to Mexico Tony Garza told Alfredo Corchado in an article published in Americas Quarterly earlier this year.

They’ve known from the beginning that the border has been anything but nonexistent. They’ve lived through its industrialization (or, as some might put it, militarization) — the fences, the expansion of Border Patrol, the surveillance.

“I’ve lived on the border for almost 30 years now,” says Vicki Gaubeca, director of the Center for Border Rights at the ACLU of New Mexico. “It used to be a much more fluid border, where people would cross more easily and have family on both sides. And now it just seems that we’re more separated from each other.”

But as disrupted as the lives of border residents already are, building a wall — or even starting to build a wall — would be something else. It would be permanent and destructive and implacable.

“What problem are we trying to solve?”

Already the fear of a wall is reverberating through the economies of border communities. “Individuals are coming less and less to come shop at better stores on the US side,” Gaubeca says. Developers in Brownsville, Texas, blamed the collapse of a planned multimillion-dollar development in the town on the fence that the government was building along the border in the Rio Grande Valley.

The border is a region, and the people who are living there don’t particularly want to be walled off from each other. Even Republican voters who live within 350 miles of the border — the people whom the president supposedly wants to protect — are much more ambivalent about it than those farther away.

“A lot of border communities think, ‘Net migration is zero; there are already so many resources that we have’” for border security, Gaubeca says. “What problem are we trying to solve?”

The benefits of building a wall across the border are questionable at best — it’s not clear whether doing more will be more effective than what already exists, or if the government is paying enough attention to make it more effective.

But the benefits won’t show up until the end of what promises to be a very long and slow process. It’s entirely possible that the effort will be started and then abandoned — or that the administration will abruptly shift to a “virtual wall” in an effort to claim an easier win.

That might prevent some of the fallout from a wall — the environmental danger, the money spent in court cases. It won’t work to reknit sundered halves of communities. The disruption of the border, as a region, is ongoing. Even considering a wall has symbolic power there. And every incremental step to turn the wall from symbol into reality works a little harder.