President Trump is still locked in a heated battle with congressional Democrats over funding for a border wall between U.S. and Mexico, telling reporters Friday that he believes the ongoing partial government shutdown could continue for over a year. But he acknowledged that there is another way to get the wall built without negotiating for $5.6 billion in funding from Congress. Mr. Trump said that he was considering calling a national emergency at the border so that the wall could be built without congressional approval.

"I can do it if I want," Mr. Trump told reporters in the Rose Garden after meeting with House Speaker Nancy Pelosi, Senate Minority Leader Chuck Schumer and other congressional leaders. "I may do it."

Mr. Trump made the case in his post-meeting address-turned-press conference that not funding a border wall was a critical matter of national security, arguing that drug dealers and human traffickers were taking advantage of the gaps on the border where no fence exists. Vice President Mike Pence also spoke briefly, saying that the country is "in the midst of a crisis on our southern border."

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If Mr. Trump called a national emergency, he would have the unilateral authority to build the wall. Although he has repeatedly claimed that Mexico would pay for the wall to be built, the money would come from American taxpayers if wall funding is approved by Congress or if it is used in a national emergency.

A national emergency is one of the conditions under which Pentagon funds could be used to build the wall. It's unclear how much of the Pentagon budget could be used for a national emergency.

One option would be to have the Army Corps of Engineers build it. Despite its name, the Corps is made up almost entirely of civilians who administer construction contracts, so troops wouldn't actually be building the wall.

Mr. Trump reiterated his claim that Mexico will indirectly pay for the wall thanks to the increase in revenue as a result of the newly negotiated U.S.-Mexico-Canada Trade Agreement. The agreement has not yet passed Congress.

"We could call a national emergency and build it very quickly. That's another way to do it. But if we can do it through a negotiated process, that's better," Mr. Trump said about building the wall. He also said that the meeting with congressional leaders was "productive."

Congressional Democrats are refusing to provide funding for the wall. Pelosi and Schumer painted a more dour picture of their meeting with Mr. Trump than the president did.

"We are committed to keeping our border safe," Pelosi said after the meeting. "We can do that best when government is open. We made that clear to the president."

"We made a plea to the president once again: don't hold hundreds of thousands of federal workers hostage," Schumer said, adding that Mr. Trump has said that he would allow a shutdown for an extended period of time. "So we told the president we needed the government open. He resisted."

David Martin contributed reporting