Republican Senator Mitt Romney has revealed that he won't run for re-election in 2024

US Senator Mitt Romney has revealed that he won't seek re-election in 2024, capping his long career in politics by bashing his own party's voters and criticizing the leadership skills of President Joe Biden and former President Donald Trump.

Romney  announced his decision in a video message on Wednesday, saying he will step down as a Republican senator from Utah after completing his current term in January 2025. Now 76 and more than a decade removed from his failed run for president in 2012, the former private-equity executive and Massachusetts governor said he's prepared to move on after 25 years in public service.

"At the end of another term, I'd be in my mid-80s," Romney 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 has been a prominent voice in the Republican Party's neoconservative wing, clashing with Trump's populist faction and promoting ever-higher Pentagon spending. Just last month, he claimed that massive military aid for Kiev had been the best defense investment in US history because the Russia-Ukraine conflict was degrading Moscow's forces while only Ukrainian forces - and not Americans - were being killed.

The next generation of leaders will have to deal with several critical challenges, including soaring national debt, climate change and the "ambitious authoritarians of Russia and China," Romney said. "Neither President Biden nor former President Trump are leading their party to confront those issues."

Among the countries with the world's 10 largest military budgets, the US outspends the other nine nations combined. Still, Romney said that when it comes to confronting the China-Russia threat, Biden "underinvests" in defense while Trump "underinvests in our alliances."

Speaking to reporters after his announcement, Romney conceded that it may take a decade for the "wise wing" of the Republican Party to overtake the populists in terms of voter support. 

"There's no question that the Republican Party today is in the shadow of Donald Trump," he said. "He is the leader of the greatest portion of the Republican Party. It's a populist, demagogue portion of the party. Look, I represent a small wing of the party. I call it the wise wing of the Republican Party."

Republicans can only win the support of young voters if they resume talking about policies and issues that make a difference in the lives of Americans, rather than talking about "resentments of various kind and getting even and settling scores and revisiting the 2020 election," Romney insisted, adding that "populism doesn't work."

Romney made history when he voted to convict Trump in the then-president's first impeachment trial in February 2020. He was the first US senator ever to vote to convict a president from his own party. The following year, he was one of seven Republican senators who voted to convict after Trump was impeached for allegedly instigating the US Capitol riot.