Donald Trump has slammed US senator Mitt Romney as a “failed presidential candidate” after he became the sole Republican to vote to convict the president in the Senate impeachment trial over abuse of power.

Despite a majority of senators expressing unease with Trump’s pressure campaign on Ukraine, on Wednesday the president won impeachment acquittal. 

While two-thirds guilty votes were needed to convict the president – who was accused of abuse of power and obstruction of Congress’ investigation into his alleged dealings with Ukraine – and remove him from office, the final tallies fell far short. 

The Senate, which is run by Trump’s Republican party, voted to acquit him 52-48 on abuse of power charges and 53-47 on obstruction of Congress. 

But Romney – who was the Republican party’s 2012 presidential nominee – was the only Republican to vote to oust Trump from office. 

In an emotional speech on the Senate floor,  Romney said: “Corrupting an election to keep one’s self in office is perhaps the most abusive and destructive violation of one’s oath of office that I can imagine.”

Announcing his decision, the senator said he believed Trump was guilty of “an appalling abuse of public trust” when he pressured Ukraine’s leaders to investigate political foe Joe Biden.

Romney said that, as a “profoundly religious” person, he was bound by the oath senators took to administer impartial justice. “My faith is at the heart of who I am,” he said.

However, he did not vote to convict Trump with the second charge of obstruction of Congress.

He is the first senator in US history to vote to convict a member of his own party in an impeachment trial. President Bill Clinton was acquitted in 1999 and Andrew Johnson in 1868.

Trump, unsurprisingly, did not take his vote lightly.

Reacting to the news Romney had voted against him, Trump tweeted: “Had failed presidential candidate @MittRomney devoted the same energy and anger to defeating a faltering Barack Obama as he sanctimoniously does to me, he could have won the election.

“Read the transcripts!” he added.   

However, Romney won support from some Democrats.

While representative Ted Lieu called Romney’s vote “a profile in courage”, his Congress colleague Sylvia Garcia said he had demonstrated “great moral courage and conviction”. 

In the UK, Labour MP David Lammy tweeted: “This is what putting country before party looks like. Good for Mitt Romney.”