Utah Senator Mitt Romney, the 2012 Republican presidential candidate and one of his party's staunchest critics of Donald Trump, announced Wednesday that he will not seek another term in the Senate.

"I have spent my last 25 years in public service of one kind or another," the 76-year-old Romney said in a video message.

"At the end of another term, I'd be in my mid-eighties," he said. "Frankly, it's time for a new generation of leaders.

"They're the ones that need to make the decisions that will shape the world they will be living in," Romney said.

Romney, who lost the 2012 White House race to Democrat Barack Obama, was elected to the Senate from Utah in 2018. He said he will complete his term, which ends in January 2025, but will not seek reelection.

Romney has been one of the leading critics of Trump in the Republican Party. He was the only Republican member of the Senate to vote twice to convict the former Republican president in impeachment trials.

Trump was impeached twice by the House of Representatives, once for seeking political dirt on Democrat Joe Biden from Ukraine and the second time for his role in the January 6, 2021 attack on the US Capitol.

Trump was acquitted both times by the Senate.

In his video message, Romney was critical of both the 77-year-old Trump and the 80-year-old Biden.

"We face critical challenges -- mounting national debt, climate change, and the ambitious authoritarians of Russia and China," he said. "Neither President Biden nor former president Trump are leading their party to confront them.

"The next generation of leaders must take America to the next stage of global leadership," he said.