A two-thirds majority vote is needed in the 435-member House of Representatives and the 100-seat Senate, which appear able to strike down a Trump veto for the first time.
The $740.5 billion National Defense Authorization Act was passed this month by the Democratic-controlled House and the Republican-majority Senate.
It passed by 335 votes to 78 in the House and 84 to 13 in the Senate.
But the NDAA was vetoed by Trump because it did not repeal Section 230, a federal law that provides liability protection to internet companies, and sought to strip several US military bases of the names of generals who fought for the pro-slavery South in the 1861-65 US Civil War.
The House is to vote to override Trump’s veto later Monday and Democrats are optimistic they have enough Republican support to do so. The Senate will take the matter up on Tuesday.
For a real estate tycoon who prides himself as a master negotiator, the past few days have been an exercise in humiliation.
Trump threatened for days not to sign the Covid-19 relief and spending bill that had been hammered out by his own treasury secretary and had received broad bipartisan support in Congress.
Trump’s surprise move risked shutting down the government from Tuesday and depriving millions of Americans of economic relief badly needed during the pandemic.
He finally backed down and signed the bill on Sunday evening at his Mar-a-Lago club in Florida out of the sight of television cameras.
In an attempt to save face, Trump released a statement airing his grievances about the November 3 election and claiming that he had obtained a number of concessions.
‘Stop the Insanity’
The strange episode highlighted the degree to which Trump has become isolated as he rails on Twitter about his election loss to Democrat Joe Biden.
In a sign of his waning influence, the Rupert Murdoch-owned New York Post, one of Trump’s most ardent supporters, published an editorial late Sunday telling him to “Stop the Insanity” and acknowledge he lost the election.
“Mr. President, it’s time to end this dark charade,” the newspaper said. “We understand, Mr. President, that you’re angry that you lost.
“But to continue down this road is ruinous,” the Post said. “If you insist on spending your final days in office threatening to burn it all down, that will be how you are remembered.
“Not as a revolutionary, but as the anarchist holding the match.”
Trump’s Twitter feed was uncharacteristically silent on Monday morning as he left Mar-a-Lago for another round of golf at the nearby Trump International Golf Club.