WASHINGTON — A day after President Donald Trump threatened to have the military build his wall along the southern border, Rep. Adam Smith, who is expected to become the chairman of the House Armed Services Committee, said he can use the position to block such a move — with Republican help.

“We can certainly put legislation in that says no Department of Defense money should go toward the wall, and that would preclude using our soldiers as part of the effort to build it,” said Smith, D-Wash. “I think there is some bipartisan support for that idea precisely because Republicans see greater defense needs.”

In comments during a breakfast with reporters on Wednesday, Smith also said Trump would be breaking his single biggest campaign promise: that Mexico, and not the United States, would pay for the wall — an assertion Smith called “insane.”

“His campaign promise is that Mexico would pay for the wall, so why in the name of God are we shutting down the U.S. government because we won’t pay for it? Why is he breaking his promise?” Smith said.

With a partial government shutdown looming for Dec. 21, the president is pressing Democratic leaders on Capitol Hill to provide $5 billion to fund his border wall. Democrats are backing plans that would allocate $1.6 billion for the project.

On Tuesday, Trump got into a televised Oval Office dustup with House Minority Leader Nancy Pelosi, D-Calif., and Senate Minority Leader Chuck Schumer, D-N.Y., over a multi-agency appropriations legislation that would avert the shutdown. There, Trump threatened that the military will build the remaining sections if Democrats withhold their support.

“The wall will get built,” he insisted.

In an early morning series of tweets ahead of the meeting, Trump fumed over the budget fight.

“If the Democrats do not give us the votes to secure our Country, the Military will build the remaining sections of the Wall,” Trump wrote. “They know how important it is!”

Politico reported that Senate Armed Services Chairman Jim Inhofe, R-Okla., suggested Tuesday he would be open to supporting using defense funds for a border wall, “as long as it doesn’t diminish the amount of money that’s going to go for war fighting.”

But by the end of the the day, a Pentagon spokesman said in a statement that “there is no plan” for the military to build sections of a border wall. However, Army Lt. Col. Jamie Davis added that the military may have the power to fund “barrier projects” in national emergencies or to counter the drug trade.

But that too is up for debate. The Senate Armed Services Committee’s ranking member, Sen. Jack Reed, is one of four Democrats pushing back after the Navy initiated studies on building more than 31 miles of barriers along the Barry M. Goldwater Range near Yuma, Arizona.

A Dec. 10 letter from Reed, D-R.I., and other lawmakers called the studies "wasteful and unjustified expenditure.” The other signatories included Dick Durbin, D-Ill., vice chairman of the Defense Appropriations Subcommittee; Patrick Leahy, D-Vt., vice chairman of the Appropriations Committee; and Brian Schatz, D-Hawaii, ranking member of the Military Construction, Veterans Affairs and Related Agencies Subcommittee.

“We believe the Department of Defense lacks any authorization or appropriations needed to move this project into any stage of construction during fiscal year 2019,” the authors wrote, adding that it contradicts guidance that the Pentagon focus on lethality and affordability.