WASHINGTON – The Pentagon is preparing options to build barriers on the southern border in the event that President Donald Trump declares a national emergency there, the latest indication such a move is gaining traction within the administration.

"The Department of Defense is reviewing available authorities and funding mechanisms to identify options to enable border barrier construction," said Navy Capt. Bill Speaks, a Pentagon spokesman. "As there has not been such a declaration made, it would be inappropriate to comment further on those efforts."

Trump is considering a declaration of a national emergency as a way to free up funds for a border wall if talks with Democrats fail to yield a deal on his signature issue.

Trump's declaration of an emergency at the southern border would allow the Army Corps of Engineers to design barriers and allow contracts to build them. Lt. Gen. Todd Semonite, who commands the corps, accompanied Trump on his trip Thursday to tour the border in Texas, according to the White House.

Trump suggested Thursday that the declaration could happen at anytime. Talks to end the partial shutdown of the federal government between Trump and Democratic leaders fell apart Wednesday over border security.

“If this doesn’t work out, probably I will do it – I would almost say definitely,” Trump said. “We have plenty of funds if there’s a national emergency.”

Vice President Mike Pence said on Capitol Hill Thursday afternoon that Trump is determined to build a wall on the border.

“The president believes he has an absolute right to declare a national emergency,” Pence said. “The president is going to get this done one way or the other.”

Those funds would come from the Pentagon's budget for construction projects approved by Congress but not yet spent.

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Texas Rep. Mac Thornberry, the top Republican on the House Armed Services Committee, said in an interview that he opposed diverting money from the Pentagon's, or any other department's, budget to pay for the barriers. Diverting the money from the military would prevent it from, for example, building barracks to house troops.

The $5.7 billion Trump seeks would build 234 miles of barriers. Thornberry said he supports improved security at the border but not at the military's expense.

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The Army Corps of Engineers would probably be tasked with the project, Thornberry said. The corps would design the barriers and contract with construction firms to build it.

"My sense is that the president has a lot of discretion in this area," Thornberry said.

Democrats vowed to challenge the declaration in court.

“I urge President Trump not to siphon taxpayer money away from military construction or family housing or vital waterway infrastructure for his wall,” Rhode Island Sen. Jack Reed, the top Democrat on the Armed Services Committee, said Thursday night. “If congressional Republicans go along with this so-called emergency, future presidents will undoubtedly try and make similar end runs around Congress’s constitutional authority. So I hope my colleagues on both sides of the aisle will take the long view and do what is best for our nation, not just one Administration.”

Sen. Doug Jones, D-Ala., a member of the committee, said Thursday that he hopes Trump doesn’t declare an emergency and divert military money to build a wall.

“Congress is concerned about the overreach, and I think the American public is concerned about the overreach of the executive branch of government right now,” Jones said.

Contributing: Eliza Collins, David Jackson and Deborah Barfield Berry