WASHINGTON — Wearing a "Make America Great Again" campaign hat, and criticizing his Democratic antagonists in Congress and their 2020 presidential hopefuls, President Donald Trump on Thursday made the case again for a border wall during a roundtable with law enforcement officials near the U.S.-Mexico line in McAllen, Texas.

"They say a wall is medieval. So is a wheel," Trump said of his critics. "A wheel works and a wall works."

Trump mostly listened to praise from participants, including Sens. John Cornyn and Ted Cruz, R-Texas, and presentations from law enforcement officers who used seized drugs, guns and money to illustrate their points about dangerous contraband being brought across the border.

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Several of the visual aids were seized at points of entry, and one picture used in a presentation was from a tunnel that the officer said was taken near a point where there is currently a barrier. Trump's Democratic critics have said that a wall will not be effective because most of the undocumented immigrants, illicit drugs and ill-gotten money entering the U.S. aren't coming through gaps in the southern border.

When Trump spoke, his remarks were aimed squarely at Democrats, whom he accused of politicizing the issue of border security in a misguided attempt to score points with voters.

"They think it’s good politically. I think it’s a disaster" for them, he said. "I’m not doing it for politics."

Reviving a theme from a central tenet of his campaign for Republican candidates in last year's midterm elections, which flipped the House into Democratic hands and increased the GOP majority in the Senate by two seats, Trump charged that Democrats are embracing crime by refusing to give him the money he needs to build a wall.

"Nobody’s going to win the battle of 'strong borders and no crime' as opposed to 'open borders and crime doesn’t matter,'" he said.

Trump has asked Congress for $7 billion in funds for border security and humanitarian assistance, including $5.7 billion for the wall. Last year, a Congress led by Republicans in both chambers failed to enact spending bills with money for the wall, and the new Congress is stuck at an impasse with Trump over that line item. As a result, portions of the federal government have been shut down since Dec. 22.

As he left for the border Thursday morning, the president told reporters at the White House that he "probably" would declare a national emergency if he couldn't get Congress to agree to fund the wall.

"I'm not prepared to do that yet, but if I have to, I will," he said. "If this doesn't work out, probably I will do it. I would almost say definitely."

In Texas, Trump said the outcome of the wall fight is central to the next election.

"All they’re doing is looking at 2020 and they figure they can’t win maybe they can do this or they can come up with some other issue," he said. "I won’t consider myself to have that great achievement unless we can straighten out your border, and we’re working on it."