Former Massachusetts Governor Bill Weld has announced his candidacy to challenge US President Donald Trump for the 2020 Republican presidential nomination.
Weld, 73, who served two terms as governor, from 1991-1997, enters as a long-shot candidate against an incumbent president who has remained popular within his party.
Weld had said in February he planned to challenge Trump.
"I really think if we have six more years of the same stuff we've had out of the White House the last two years that would be a political tragedy," he said on CNN.
"So I would be ashamed of myself if I didn't raise my hand and run."
Weld's challenge marks the first against Trump by a member of his own party.
Other Republicans have publicly flirted with their own challenges, including former Ohio Governor John Kasich, one of the many Republican candidates whom Trump defeated for the party's presidential nomination in 2016.
But Republican leaders have signalled little tolerance for intra-party fights as Trump gears up for a potentially challenging bid for a second term.
"Any effort to challenge the president's nomination is bound to go absolutely nowhere," the Republican National Committee said in statement responding to Weld's announcement, noting that its operation and the Republican Party are firmly behind Trump.
Weld, a former prosecutor and the vice presidential candidate in 2016 on the Libertarian ticket, has been a consistent critic of Trump.
He told CNN that he does not plan to mount an independent bid if unsuccessful.
"Right now, all there really is coming out of Washington is divisiveness," he said on CNN, calling both parties responsible but pointedly adding, "the grand master of that is the president himself."
Trump's campaign raised more than $30 million in the first quarter of 2019, far outpacing the sums raised by individual Democratic candidates during that period.
The fundraising underscores the willingness of Republican donors to invest in Trump's re-election bid.
Australian Associated Press