"The 5.6 billion is such a small number," Trump added, citing the figure he wants for wall funding. "We're talking about national security. This isn't just a border."
His comments, several of which were inaccurate, seemed certain to deepen the stalemate that caused about a quarter of the federal government to close just before Christmas, with no end to the impasse in sight.
Trump himself seemed to shrug off any urgency to bring a close to the shutdown, which has kept hundreds of thousands of federal workers at home, shut down some services and left national parks in disarray. The budget lapse would continue "as long as it takes," he said.
In one of a series of false or unsupported assertions, Trump said that there were between 30 million and 35 million undocumented immigrants in the United States, roughly three times larger than the estimate of most experts.
He also parried complaints from Democrats who've called the wall immoral by remarking, "Then we have to do something about the Vatican, because the Vatican has the biggest wall of them all."
Democrats prepared for the White House gathering by saying they had no plans to be lectured with inaccurate information and would continue to challenge the President.
"It's not often the President gets to hear people tell him when he's wrong. Democrats intend to do that today," Justin Goodman, spokesman for Senate Minority Leader Charles Schumer said.
Earlier, in a Twitter post, Trump made two other false claims about the wall.
He wrote that Mexico would be paying for the wall under the parameters of a trade deal he has tentatively inked with Mexico and Canada.
This is not true. That deal has not been approved by Congress, which means the parameters of the pact are not in effect. And even if the trade agreement is approved, it would not in any way create a stream of money designated for the construction of a border wall.
The second false point in Trump's Twitter post is his statement that "much of the Wall has already been fully renovated or built".
This is also not true. The US-Mexico border is roughly 3220km long. The US$5.6 billion Trump is demanding would finance about 320km of wall, and less than 160km has already been constructed or renovated, according to Department of Homeland Security officials.
And there were growing signs that members of the Republican Party did not support Trump's approach.
Incoming-Senator Mitt Romney, R, penned an editorial in the Washington Post, slamming Trump's governing style and promising to challenge the President when he sees fit. And Senator Lamar Alexander, R, in a separate op-ed, wrote that Trump should act more like former President Barack Obama did in 2015 and proactively seek a bipartisan solution to the shutdown.
"Government shutdowns should be as off-limits to budget negotiations as chemical weapons are to warfare," Alexander wrote. "Nevertheless, we are stuck in one."
The shutdown began after Trump rejected bipartisan congressional efforts to fund many operations until February 8, insisting that any deal must contain money for the construction of a border wall.
His demand infuriated many Republicans who had been working to avoid a shutdown, but most have followed his lead and are insisting Democrats broker some sort of compromise.
Schumer and incoming House Speaker Nancy Pelosi prepared to attend the meeting with Trump as Democrats remain unified in their opposition to extending additional taxpayer money to finance a wall on the Mexico border. The meeting is taking place before Democrats retake control of the House tomorrow, heralding a massive power shift in Washington after two years of unified Republican control.
The current shutdown is the longest since a 16-day partial shutdown in 2013 over the Affordable Care Act.
