President Trump takes his case for border security directly to American voters Tuesday night in a prime-time address aimed at enlisting the public’s help in convincing Congress to pony up billions of dollars for his border wall.

The president will then jet to the border on Thursday for an up-close look at what he says is a dire security crisis.

He’s pondering declaring a national emergency and enlisting the military to construct the wall, circumventing congressional Democrats who have insisted they won’t approve any new money for his border-barrier vision.

SEE ALSO: Pelosi, Schumer demand equal airtime for Democrats after Trump address

Vice President Mike Pence, briefing reporters Monday, said no decision has been made and they’re still studying the legal justification.

He said they’d prefer to get a deal done on Capitol Hill, but their outreach has been met with silence as the partial government shutdown stretches into its third week.

“When are the Democrats going to start negotiating?” Mr. Pence said. “There is a crisis at the southern border. We just need the Democrats to start negotiating.”

Mr. Pence and other top administration officials held talks with Democratic congressional staffers over the weekend, and he said the president has invited Democratic leaders back to the White House this week for new talks, but so far there has been no response.

“We hope they take us up on it,” he said.

Democrats have been adamant there can’t be any deal until Mr. Trump agrees to reopen the government. About 350,000 federal workers have been furloughed and another 420,000 are working without pay, according to a Senate estimate.

And Democrats warned Mr. Trump against any emergency declaration.

“The president has no authority to usurp congressional authority of the purse. Congress must appropriate funds,” said new House Judiciary Committee Chairman Jerrold Nadler, New York Democrat. “The courts should not permit it, and I do not believe the courts will permit it.”

He said such a move would be tantamount to the president making “himself a king and a tyrant,” and he warned the public to be wary of the president’s speech.

“I expect the president to lie to the American people,” he said.

Mr. Nadler was speaking outside a Border Patrol facility in New Mexico, where he and a group of fellow Democrats were investigating the death on Christmas Eve of an 8-year-old Guatemalan boy who’d jumped the border with his father.

The government shutdown is now in its third week with no sign of either side relenting.

“No progress has been made because the president doesn’t want to negotiate in good faith to end the shutdown,” said new House Appropriations Committee Chairwoman Nita Lowey, New York Democrat, on WNYC radio. “We have repeatedly given proposals and the Republicans, led by Trump, keep refusing.”

Administration officials say there is general agreement with Democrats on providing an additional $800 million for urgent humanitarian needs at the border, including enhanced medical supplies and services.

Mr. Pence said there is also agreement with Democrats on spending $675 million for “non-intrusive” inspection technology to search vehicles for drugs, weapons and other illegal materials as they come through official border crossings.

But Republicans said Democrats haven’t budged on the administration’s request for $5.7 billion for a barrier at the border, $563 million for 75 more immigration judges, or $211 million to hire another 750 Border Patrol agents.

Homeland Security Secretary Kirstjen Nielsen told reporters that the crisis at the border has grown significantly worse since last February, with about 2,000 illegal immigrants per day apprehended crossing the border.

“There’s a real sense of urgency. The crisis is getting worse,” she said.

She points to growing drug seizures and arrests of criminals, gang members and terrorists by Customs and Border Protection personnel as evidence of the need for a wall.

Democrats, though, said the hard drugs are coming through border crossings, while those on terrorist watch-lists are mostly being stopped at airports.

They say the families and unaccompanied children being caught are refugees fleeing poverty and violence in their home countries and should be allowed to apply for asylum.

“This is a humanitarian crisis. This is not a national security crisis,” said Rep. David Cicilline, Rhode Island Democrat, during Democrats’ border trip Monday. “The president is attempting to use this to make some argument about the safety of the American people. It’s just not true.”

NBC, ABC, CBS and Fox all will carry the president’s address.

The White House has asked networks to set aside at least eight minutes for the Oval Office speech.

The four major networks aired President George W. Bush’s prime-time address on immigration in 2006 but did not air one by President Obama in 2014. At the time four years ago, network executives told Mr. Obama that his address was considered “overtly political.”

⦁ David Sherfinski and Stephen Dinan contributed to this article.