Vice President Mike Pence says the White House is looking into the legality of declaring a national emergency to circumvent Congress and begin construction on President Donald Trump’s long-promised Southern border wall.

Pence said Trump continues to weigh the idea but has yet to make a decision.

A DoD official said the Pentagon is looking at options in case the president declares a national emergency on Tuesday.

The comments came as Pence briefed reporters on the 17th day of the partial government shutdown. He was joined by Homeland Security Secretary Kirstjen Nielsen and other senior administration officials.

Pence says the president has invited Democratic leaders Chuck Schumer and Nancy Pelosi back to the White House to continue their discussions. But he says Trump isn't budging on his demand for billions for his border wall.

As of late Monday, there were a lot of unanswered questions, such as how much money the Pentagon has remaining in unobligated military construction funds that could be reprogrammed to support a wall. Typically Congress has to approve funds getting reprogrammed to pay for a federal project other than the project they were authorized for.

The Pentagon was still looking at whether that would be the case if a national emergency is declared, another DoD official said. Both officials spoke on the condition they not be named.

There are 2,350 active-duty and about 2,200 National Guard members currently deployed to the border, one of the officials said.

Pence said he and Nielsen will be visiting the Capitol Tuesday and Wednesday to brief House and Senate members.

Trump says he will address the nation Tuesday night about what he says is a “crisis” at the U.S.-Mexico border.

Trump’s prime-time address will come amid the partial government shutdown caused by his insistence that Congress give him more than $5 billion to build a wall on the border.

Trump tweets that he will address the nation at 9 p.m. Eastern time Tuesday.

Trump also plans a trip Thursday to the southern border to highlight his demands for the wall. White House press secretary Sarah Huckabee Sanders said Trump will “meet with those on the front lines of the national security and humanitarian crisis.”

Pelosi intends to begin passing individual bills to reopen agencies in the coming days, starting with the Treasury Department to ensure people receive their tax refunds.

Reporter Tara Copp contributed to this report.