WASHINGTON — House legislation extending surveillance authorities that the FBI sees as vital in fighting terrorism was thrown into doubt Wednesday as President Donald Trump threatened a veto, and Republican leaders and top liberal Democrats said they would oppose it.

Ahead of a House vote scheduled for Wednesday evening, Trump said explicitly for the first time that he would veto the measure. A similar version of the legislation had drawn bipartisan support just weeks ago.

“If the FISA Bill is passed tonight on the House floor, I will quickly VETO it,” Trump tweeted, using the acronym for the Foreign Intelligence Surveillance Act. “Our Country has just suffered through the greatest political crime in its history. The massive abuse of FISA was a big part of it!”

Trump had earlier suggested he’d oppose the measure, prompting Republicans who once backed the deal to follow Trump’s lead and say they would now vote against it.

The leaders of the Congressional Progressive Caucus, which has about 70 Democratic House members, also said they would oppose the legislation, saying it lacked curbs on online surveillance without warrants. Combined with strong GOP opposition, their defiance of House Speaker Nancy Pelosi, D-Calif., suggested there might be enough dissent to sink the bill.

“We cannot in good conscience vote for legislation that violates Americans’ fundamental right to privacy,” said the caucus’ leaders, Reps. Pramila Jayapal, D-Wash., and Mark Pocan, D-Wis.

The legislation first passed the House in March with broad bipartisan support after Attorney General William Barr negotiated a deal with Republican and Democratic House leaders.

But that consensus crumbled Wednesday after the Justice Department came out against the bill, which was amended by the Senate. The Justice Department’s statement, by Assistant Attorney General Stephen Boyd, urged Trump to reject the bill.

Hours later, House Republican Leader Kevin McCarthy, R-Calif., said it was time to take a “pause” on the legislation.

The new impasse raised the potential for the surveillance powers to remain expired indefinitely.

Democratic leaders said they would move forward with a vote anyway, arguing that very little had changed since 126 Republicans, including McCarthy, voted for it in March.

Trump, still seething over the Russia investigation, implored all House Republicans in a Tuesday evening tweet to vote no “until such time as our Country is able to determine how and why the greatest political, criminal, and subversive scandal in USA history took place!”