WASHINGTON, D.C. — The Senate on Wednesday acquitted President Donald Trump of abusing the power of his office and obstructing Congress’ investigation into his conduct, ending the third presidential impeachment trial in American history.

Republicans and Democrats had appeared to be marching toward an entirely party-line vote. But Sen. Mitt Romney, R-Utah, the party’s presidential candidate eight years ago, became the only GOP lawmaker to join Democrats in voting to convict the president for what he called “an appalling abuse of public trust.”

For Trump, the Senate verdict allows him to declare victory as he turns toward a reelection bid. But unlike any president in modern history, he will run under the stigma having been impeached by the House — a move with unknown political consequence.

Moreover, although Romney stood alone among Republicans in voting to convict Trump, he had company among his party’s senators in rejecting Trump’s repeated claim that his actions were “perfect.” More than a half dozen Republican senators have said they believe Trump’s actions regarding Ukraine were wrong, although they felt the conduct should not result in his removal from office.

The Senate voted 48-52 on the first article of impeachment, abuse of power, and 47-53 on the second article, obstruction of justice. Romney voted against the second article. Both articles required 67 votes for approval.

The House impeached Trump in December for withholding nearly $400 million in U.S. aid to Ukraine while pressing the country’s leaders to announce investigations into his political rivals, including former Vice President Joe Biden.

Romney’s decision allows Democrats to claim bipartisan support — thin as it may be — for convicting Trump, and prevents the president from claiming his party was united in eschewing impeachment.

“Corrupting an election to keep oneself in office is perhaps the most abusive and destructive violation of one’s oath of office that I can imagine,” said Romney, speaking on the Senate floor before the vote.

Rep. Adam B. Schiff, D-Calif., the lead House impeachment manager who presented the case to the Senate, said that Democrats will remain “vigilant” in their oversight of the president.

“There is a risk that he becomes even more unbounded,” Schiff said of Trump in an interview with the Los Angeles Times before the vote. “We succeeded in exposing his misconduct and stopping the plot, but his plotting continues and we’re going to have to be vigilant.”

During his closing arguments earlier this week, Schiff had asked aloud if there would be even one Republican senator to vote for conviction. After Romney’s announcement, Schiff tweeted Wednesday: “And there is.”

Romney acknowledged that he could face the wrath of the president, his party and some of his constituents.

“Does anyone seriously believe that I would consent to these consequences other than from an inescapable conviction that my oath before God demanded it of me?” he said. Later, he told Fox News it was the most difficult decision of his life and predicted he would pay a political price. “It’s going to get very lonely,” he added, referring to the political backlash.

Democrats praised Romney’s decision. “Mitt Romney has restored my faith in this institution and my faith in the basic idea that political courage can exist in a polarized world,” said Sen. Brian Schatz, D-Hawaii.

The 12-day trial is the shortest in presidential impeachment history, and the only one that did not include subpoenas for witnesses or documents. Democrats say that exclusion delegitimized the process.