President Donald Trump continues to claim that his signature promise from 2016 — to build a U.S.-Mexico border wall — is well on its way, and that hundreds of miles will be completed by the end of 2020, when it’s time for voters to decide whether to re-elect him as president. Chants at his rallies have gone from "build the wall" to "finish the wall."

But despite the chants and Trump’s repeated assurances that a border wall is under construction, what’s been achieved so far doesn’t reflect his campaign promise.

Before Trump became president, 654 miles of the nearly 2,000-mile U.S. Mexico border had primary barriers. As of today, that hasn’t increased.

To date, the administration has replaced about 60 miles of dilapidated barriers with new fencing. And a major component of Trump’s pledge — that Mexico would pay for the wall — hasn’t been part of the equation. U.S. taxpayers have paid the cost.

Building a border wall hasn’t been as easy as Trump might have hoped. Some key issues impede his pledge:

• Opposition from Democratic lawmakers who say the wall is ineffective and that appropriating funds for it is wasteful;

• Unsuccessful negotiations with Democratic lawmakers to get money for the wall in exchange for protections for so-called "Dreamers";

• Some of the property along the border is privately owned, and there are Texans unwilling to give it up for the wall.

• None of the wall prototypes the administration paid contractors to build in 2017 met all of U.S. Customs and Border Protection’s requirements.

Trump hasn’t built an extensive wall from sea to shining sea, but he’s still seeking ways to get barriers up while giving the impression that his promise is already taking shape. Earlier this year, citing an "invasion" at the border, he declared a national emergency in order to access money from the military’s budget to build the wall. Congress wasn’t giving him the money he wanted.

Customs and Border Protection told PolitiFact that since January 2017, the agency has received about $6.2 billion to build 334 miles of "new border wall system." That includes steel-bollard barriers, all-weather roads, lighting, cameras, and other surveillance technology.

About 224 of those 334 miles would have new barriers in place of existing structures. So far, approximately 60 miles of replacement barriers have gone up. The $6.2 billion comes from the departments of Homeland Security and Defense, and the Treasury Forfeiture Fund.

Trump at times has seemingly acknowledged that what’s taken shape isn’t the extended mileage of barriers that his supporters and critics envisioned.

"When we rip down and totally replace a badly broken and dilapidated Barrier on the Southern Border, something which cannot do the job, the Fake News Media gives us zero credit for building a new Wall. We have replaced many miles of old Barrier with powerful new Walls!" Trump tweeted July 22, and sent a similar tweet a day later.

Overall, Trump has also been less vocal about Mexico paying for the wall, though in January he falsely claimed that Mexico would pay through a renegotiated North American Free Trade Agreement.

Experts on immigration and border security told PolitiFact that a border wall — or replacement fencing — likely won’t stop the recent surge of immigrants and of illicit drugs that make their way into the United States from the southern border.

The majority of opioids that are known to be smuggled across the border come in through official points of entry. And the smuggling of marijuana in between ports of entry has gone down in recent years, as some places in the United States legalize its medical and recreational use.

Most of the people now arriving at the border are families seeking Border Patrol agents to turn themselves in and ask for asylum. They are not trying to sneak in.

"It’s just not likely that this border wall will have any significant effect on the total amount of immigration," said David Bier, an immigration policy analyst at the libertarian Cato Institute. When barriers went up in the past, people found new routes, he said.

Cristobal Ramón, a senior policy analyst with Bipartisan Policy Center’s Immigration Project, told PolitiFact that the premise of a border wall is stuck in a mid-1990s to early 2000s mentality, when there were high numbers of single Mexican men coming looking for jobs and trying to evade immigration authorities.

The Secure Fence Act of 2006 passed in response to that immigration flow, Ramón said. It authorized the construction of a fence along 700 miles of the U.S.-Mexico border.

"I think the wall is fighting yesterday’s battle," Ramón said. "The assumption that if you build a wall you deter immigration is shortsighted, because it doesn’t take into account that the people arriving shifts over time."

Mark Krikorian, executive director of the Center for Immigration Studies, which favors low-levels of immigration, said Trump used the issue of the wall effectively to tap into voters’ frustration about immigration enforcement. A weakness of that pitch, Krikorian said, is that Trump gave Democrats a weapon to use against him: the ability to deny him money for the wall.

"Given the headwinds the president has been pushing against, I think they have made some useful progress," Krikorian said. Barriers are an important tool, but not the sole solution against illegal immigration— also needed are more immigration judges and more border personnel, he said.

Expedited hearings of cases could also help reduce illegal immigration, said Gil Kerlikowske, a Customs and Border Protection commissioner during the Obama administration and professor of practice at Northeastern University. If people are sent back to their country shortly after their arrival — instead of that removal process taking years — that could have a chilling effect on others who are also thinking of coming illegally, he said.

A border wall, Kerlikowske said, is an "incredibly simplistic answer to a complex problem."