In a 59-41 vote, in which 12 Republicans defied the president, the Senate passed a measure to rescind the national emergency declared by Mr Trump last month in a move widely seen as a means to circumnavigate a Congress that had rejected his demand for more than $8bn in funding for a border wall.
The House of Representatives has already passed the bill, and it now goes to the White House, where Mr Trump has vowed for the first time to use his veto powers. Indeed, Mr Trump immediately reacted to the news with a single-word tweet that said: “VETO”.
Whether there are enough numbers to overturn Mr Trump’s expected move – a two-thirds vote of both chambers of Congress is needed to override a presidential veto – is unclear.
What it certainly does is place Mr Trump’s demand for a border wall and Democrats’ refusal to fund one front-and-centre as the 2020 presidential election campaign starts to gather pace.
When Mr Trump announced the state of emergency in February, during a meandering 50-minute appearance in the Rose Garden of the White House, he claimed he was taking the measure on the grounds of national security.
“We’re talking about an invasion of our country with drugs, with human traffickers, with all types of criminals and gangs,” he said.
“I didn’t need to do this, but I’d rather do it much faster.”
Commentators pointed out that the vast majority of drugs entered the country thought its legal crossing points. Rather, critics said, the president was seizing on the issue to try and rally his base as he prepared for a tough re-election battle.
Reuters said those Republicans who defected on Tuesday by supporting the measure to end the emergency declaration, were worried about executive creep – namely, that presidents, including future Democratic ones, could seize the powers traditionally held by Congress to fund the government and use the tactic to pass their own pet programmes and schemes.
The Republican leader in the Senate, Mitch McConnell, claimed the president was “operating within existing law” and that if senators did not like the powers provided to the president under the National Emergencies Act, “then they should amend it”.
Senator Angus King, one of two Senate independents, said of the vote: “It’s an important legal statement. It tells the court this is explicitly not approved by Congress By voting this resolution Congress is reiterating we don’t approve of this expenditure.”
The vote marked the second congressional rebuke for the president in as many days.
Earlier this week, senators approved a resolution seeking to end US support for the Saudi Arabia-led coalition in the war in Yemen, rejecting the president’s allegedly fawning and unquestioning support for the kingdom. The White House has said he will also veto that measure.