President Trump is pledging a veto if Congress passes a resolution blocking his use of a national emergency declaration to fund a wall along the U.S.-Mexico border.
Mr. Trump told reporters at the White House on Friday that he would veto the resolution introduced by House Democrats earlier in the day.
“Will I veto it? 100 percent,” the president told reporters.
The move by House Democrats starts the clock on a constitutional clash between Mr. Trump and Democrats and sets up a vote by the full House as soon as next week.
The Democratic-controlled House is sure to pass the measure, although its fate in the GOP-controlled Senate is less clear.
Any Trump veto would likely be sustained, but the upcoming battle will test Republican support for Mr. Trump’s move.