“Need to stop Drugs, Human Trafficking, Gang Members & Criminals from coming into our Country,” Trump wrote with his idiosyncratic capitalization. Later in the day he added that Democrats want an “Open Southern Border and the large scale crime that comes with such stupidity.”

Democrats don’t want “open borders,” of course, but oppose the construction of the wall in part because it’s so central to Trump’s priorities. But the bigger reason Democrats oppose construction of the wall is that Trump’s arguments about what the wall will prevent are inflated or incorrect.

Illegal immigration

Consider the question of illegal immigration alone.

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Last month, Pew Research Center released updated data about illegal immigration in the United States. Since the recession, the number of undocumented immigrants living in the country is estimated to have dropped slightly, thanks largely to a slowdown in immigrants from Mexico entering the country illegally. (Note that this is not the same as immigrants entering the country illegally from Mexico.) One result? Two-thirds of those living in the United States illegally have been here for at least a decade.

So who are the new arrivals? Are they mostly people crossing the southern border illegally? No. They are mostly people who arrive in the United States on legal visas who don’t leave when they are required to. As our Chris Ingraham wrote in June, a report from the Center for Migration Studies estimated that about two-thirds of those who join the undocumented population each year are people overstaying visas.

“The number attempting to get across the Southern border is probably the lowest it’s been since at least the 1970s,” one demographer told Ingraham.

Government data suggest that in 2016 there were about 170,000 successful illegal border crossings outside of authorized border crossing points. That same year, the Department of Homeland Security estimates, 630,000 people overstayed visas.

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What’s more, those who cross the border illegally often quickly seek out law enforcement officials to make asylum claims. The Trump administration is trying to force asylum seekers to use designated ports of entry, but many of those who have crossed the border illegally in recent years have done so because the asylum process requires that someone seeking protection be in the United States when making a claim.

Drugs

Trump has tied illegal immigration to the opioid crisis specifically and illegal drug smuggling broadly. But that, too, is misleading.

In February 2017, then-Homeland Security secretary John F. Kelly — who is now Trump’s chief of staff, for the next few days — testified before Congress that most drugs that enter the United States across the border with Mexico come smuggled in vehicles or on the bodies of people crossing into the United States.

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As USA Today reported last year, moving smuggling to ports of entry by blocking or patrolling heavily used smuggling routes was intentional, making it easier for authorities to track illegal drugs. But it also meant an increase in the use of different methods, such as drug-smuggling tunnels, through which drugs still flow and which wouldn’t be affected by a wall.

A Customs and Border Protection official who spoke with USA Today argued that no wall — or anything else — would fully curtail drug smuggling.

“We can put barriers and we can slow them down but no matter what we do people are still going to try,” he said.

Human trafficking

The administration has repeatedly pointed to the horrors of human trafficking to defend its immigration policies and, in particular, its approach to dealing with children who arrive at the border. In doing so, it has also repeatedly inflated the threat posed by trafficking.

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Last month, Katie Waldman of the Department of Homeland Security released a statement claiming that “from April 19, 2018 to September 30, 2018, 507 aliens were encountered as a family unit and were separated as they were not a legitimate family unit.” The implication, similar to an implication made in June, was that U.S. law enforcement had blocked people improperly or suspiciously claiming a child as their own.

But that number included people such as children who were actually over the age of 18 and therefore not children. The number of people who were “individuals using minors to pose as fake family units” (as DHS put it in June) was 170.

In June, over a shorter time period, it had been 191. The 170 figure was 0.25 percent of all apprehensions of family units on the border during the April-to-September period.

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Nor were all of these 170 individuals necessarily attempting to smuggle children into the country as part of a human trafficking effort. Some, for example, may have been children accompanying family friends on the journey from Central America to the United States. The number of people trafficked across the border illegally is unclear — as is the number of people smuggled through ports of entry.

Crime and gangs

It’s well established by now that there’s no correlation between immigrants and crime; in fact, immigrants are less likely to commit crimes than native-born Americans.

Two different studies, covered by Ingraham this year, show further that undocumented immigrants are less likely to commit crimes than native citizens. The first study looked at conviction data in Texas finding that, while immigrants in the country illegally were more frequently convicted of crimes than legal immigrants, the rates of conviction were lower than among native-born Americans. The other study found an inverse correlation between the rate of violent crime and the density of the undocumented immigrant population — as one went down, the other went up.

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This summer, Trump claimed that at least 63,000 Americans had been killed by undocumented immigrants since Sept. 11, 2001. That figure came from rhetoric offered years ago by virulently anti-immigration Rep. Steve King (R-Iowa). That number, too, is inaccurate. It was sloppily derived from a study that looked only at federal prisoners (among whom those committing immigration-related crimes are overrepresented) and included both those here legally and illegally.

Trump also often claims that young people coming into the United States are members of the criminal gang MS-13. To address that, we can point to testimony from the acting head of Customs and Border Protection in June of last year. From 2011 to mid-2017, the agency had encountered nearly 250,000 unaccompanied minors — people under 18 — at the border. Of that group, about 159 had some gang affiliation. Fifty-six of those were MS-13, about 0.02 percent of the total.

Other arguments

It is the nature of Trump’s rhetoric that he will make debunked claims over and over and over again, without changing course. So we’ll note two other arguments that he’s made in the past — and that we’ve already debunked.

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Terrorism. Trump has claimed that the criminals crossing the border include terrorists. Earlier this month, he claimed that 10 terrorists had been caught in recent months.

There’s no evidence that’s true. In fact, a report from the State Department last year offered a sharply different assessment of the threat: There is “no credible information that any member of a terrorist group has traveled through Mexico to gain access to the United States.”

Disease. At the same time, Trump claimed that immigrants crossing into the country illegally helped spread disease. Experts who spoke with NBC News this month said that there was “no evidence” that this was happening. There have been increases in communicable diseases in immigrant populations that often stem from conditions related to their migration (such as being housed in camps), but transmission of those illnesses is generally among other members of the community.

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Cost. Then there’s the purported cost of illegal immigration. One report from an organization that supports limiting immigration pegged the annual cost at more than $100 billion, though that includes things such as the cost of educating the children of undocumented immigrants, many of whom are native-born citizens of the United States.