Trump said his lawyers had told him the action would withstand legal scrutiny "100 percent".
Trump's visit comes after negotiations between the president and Senate Democrats broke down in a contentious, 14-minute meeting that ended with the president walking out of the room after Speaker Nancy Pelosi said she would not agree to fund the president's wall if he agreed to reopen the government.
Officials have estimated that roughly one-quarter to one-third of the money, or $2.5 billion to $3 billion, could be available - less than the $5.7 billion Trump is seeking.
The White House has said the president's trip is created to allow him to meet with those individuals who are "on the front lines" of what they have called a "national security and humanitarian crisis".
President Trump on the partial government shutdown and efforts to reach a compromise on border wall funding. "The president once said that Mexico would pay for the wall", he said, playing a montage of Trump at campaign rallies.
The emergency funds had been set aside for California in the wake of devastating wildfires that tore through 1.8 million acres in the state this year, as well as Puerto Rico, Texas, and Florida as they continue to recover from 2017 and 2018's hurricanes and prepare for similar storms in the coming years.
President Donald Trump's insistence on obtaining full funding for his proposed wall along the southern border will officially result in the longest lapse in federal government funding in US history. Congressional Republicans have sounded wary of such a move and some have expressed outright opposition, while Democrats have expressed alarm.
Todd Semonite, commanding general of the Army Corps of Engineers, was traveling with Trump on Thursday.
But even some Republican lawmakers uneasy about the idea of pulling money from Army Corps projects saw few alternate options.
"While the President has broad military authorities, as the Commander in Chief, when it comes to declaring a national emergency, I can not and will not support reallocating funding we approved in a bipartisan effort in Congress for the recovery and reconstruction of Puerto Rico", Gonzalez said.
"Most conservatives want it to be the last resort he would use", Meadows said.
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