While Congress is unlikely to muster the votes to override the veto, the rebuke from some members of his own party left Trump politically wounded, at least temporarily, as immigration and his planned wall along the US southern border become a flashpoint again in the 2020 presidential campaign.
White House spokeswoman Mercedes Schlapp would not say when the veto would happen, but told reporters Friday Trump is "doing what he believes is his constitutional duty, which is to protect the American people".
But the Senate margin fell short of the 67 votes needed for a veto override. "This is not about the president or border security, in fact I support border security, I support a barrier".
Congressional critics do not appear to have the votes to override Trump's veto. Twelve Republican senators joined Democrats in rejecting the president's emergency declaration. "This will help stop Crime, Human Trafficking, and Drugs entering our Country", the president tweeted.
BREAKING: Trump Signs His First Veto Against Resolution Blocking Emergency Declaration
"The president acted well within his discretion in declaring a national emergency concerning the southern border", the Justice Department argues in the letter, a copy of which was reviewed by The Washington Post.
"I'd like to thank all of the Great Republican Senators who bravely voted for Strong Border Security and the WALL". Democrats and some Republicans challenged the declaration as a blow to the separation of powers. The House had passed the same resolution last month largely along party lines.
They included Sens. Marco Rubio, Rob Portman, Susan Collins, Lisa Murkowski, Pat Toomey, Roy Blunt, Lamar Alexander, Mitt Romney, Rand Paul, Jerry Moran, Mike Lee, and Roger Wicker. The measure ultimately passed 59-41, and Trump immediately vowed to veto.
President Donald Trump on Friday vetoed legislation attempting to strike down his declaration of a national emergency at the southern border during an Oval Office event from the White House.