Updated at 2 p.m. ET
President Trump says he is willing to declare a national emergency if Democrats don't go along with his demands for $5.7 billion for a border wall.
Trump's campaign for a border wall took him to McAllen, Texas, on Thursday for a visit to a Border Patrol station and a roundtable discussion with local officials, before he heads to the Rio Grande.
As he left the White House on Thursday morning, Trump said he has the "absolute right" to declare a national emergency in order to construct a border wall but said he prefers to continue efforts to make a deal with Congress. However, he said, "If we don't make a deal, I think it would be very surprising to me" to not declare an emergency.
Such a declaration would almost certainly be fought in court.
House Speaker Nancy Pelosi, D-Calif., sidestepped a question about the issue Thursday, telling reporters, "If and when the president does that, you'll find out how we will react."
She predicted that if the president did take that step, he would have to answer to his own party for "usurping" power.
On Thursday, Trump again said Republicans are unified in support of him on the wall, saying he hasn't "ever seen unity like this in the Republican Party."
However, several Republican senators have expressed concern over the effects of the continued partial government shutdown, now in its 20th day, and a handful of Republicans voted with Democrats in efforts to reopen the government in the House.
Trump also disputed characterizations of Wednesday's meeting with Democratic leaders, in which Trump abruptly walked out. On Thursday morning, he told reporters that "I didn't pound the table. I didn't raise my voice, that is a lie," adding, "I don't have temper tantrums. I really don't."
In her news conference, Pelosi suggested that Wednesday's White House meeting with Hill leaders was never about a serious negotiation. "I think the meeting was a setup so he could walk out," she said.
Recounting an exchange during the meeting, she said, "I said to him: You are moving the goal posts so many times they are out of the stadium."
She said the president keeps changing his demands: "I don't even know if the president wants the wall."
Democratic congressional leaders have refused to go along with Trump's demand for border wall funding, and Senate Majority Leader Mitch McConnell has refused to take up Democratic measures to fund government agencies that have run out of appropriations.
Some 800,000 federal workers have been furloughed or are working without paychecks because of the standoff. Many will be missing their first paychecks on Friday.
The FBI Agents Association, whose members are among those working without pay, sent a petition to the White House and congressional leaders warning of the effects of the shutdown on agents and their work. It says that FBI agents could face difficulty in obtaining or renewing security clearances if they miss bill payments and that "pay uncertainty undermines the FBI's ability to recruit and retain high caliber professionals."
Trump also said that despite his repeated campaign promises to build a wall and have Mexico pay for it, he didn't mean that literally.
"When I said Mexico would pay for a wall in front of thousands and thousands of people," Trump said, "obviously I never meant Mexico would write a check."
But a March 2016 memo from the Trump campaign to the The Washington Post said, "It's an easy decision for Mexico. Make a one-time payment of $5-10 billion to ensure that $24 billion continues to flow into their country year after year."
Trump also announced on Twitter that he has canceled a planned trip to Davos, Switzerland, later this month for the World Economic Forum, blaming Democrats' "intransigence" on border security.