Three Senate Democrats from conservative-leaning states who had been targeted by the White House as possible defectors voted to convict Mr. Trump, depriving the president of the chance to claim a bipartisan exoneration despite the political risk.

Senators Kyrsten Sinema of Arizona, Joe Manchin III of West Virginia and Doug Jones of Alabama all announced their decisions in the final hours before the vote ending the Senate impeachment trial, ensuring that all 47 Democrats would stick together in supporting the removal of Mr. Trump from office.

“After many sleepless nights, I have reluctantly concluded that the evidence is sufficient to convict the president for both abuse of power and obstruction of Congress,” Mr. Jones, who is facing re-election in a state that Mr. Trump won in 2016 by nearly 28 percentage points, said in a statement.

Mr. Manchin, whose state went for Mr. Trump with 70 percent three years ago, had urged a nonbinding, bipartisan censure, only to be ignored, and told reporters that he struggled deeply over his decision. “It’s a tough one guys,” he said before announcing his decision. “It’s a tough one.”

Ms. Sinema, a freshman who was one of the few Democrats to enthusiastically jump to her feet to applaud Mr. Trump at points during his State of the Union address on Tuesday night, said that in the end she could not condone Mr. Trump’s use of his office to leverage domestic political assistance from a foreign power.

“While White House attorneys claim this behavior is not serious,” she said in a statement, “it is dangerous to the fundamental principles of American democracy to use the power of the federal government for personal or political gain.”

— Emily Cochrane and Michael D. Shear