A former governor was the first to say he was challenging Donald Trump for the Republican presidential nomination.
William Weld, 73, announced that he took over the person with appearances on television news channels and simultaneously published magazine interviews.
He said, "It is time to return to the principles of Lincoln – equality, dignity and opportunity for all.
"There is no greater reason on earth than to preserve what makes America really great, I am ready to lead this fight."
The former Massachusetts governor, known as Bill, last won a 1994 election when he was re-elected despite a democratic state with a landslide.
He ran again in 1996 for the governor, but lost to John Kerry and tried again in 2005 in New York, without success.
In 2016, he served as vice presidential candidate for the Libertarian Party – a right-wing party dedicated to free market principles and personal freedom.
His challenge will be the first time a reigning president has faced a notable major bid since George HW Bush in 1992
Mr. Weld faces a difficult task – while Mr. Trump's general approval ratings are poor, he remains popular with Republican voters.
The Republican National Committee (RNC) has issued a non-binding resolution declaring its full support for Trump.
His 2020 election campaign reportedly earned $ 30 million in the first quarter of this year.
Mr Weld said that Mr Trump left the nation in 'grave danger' and that his priorities were 'more for the promotion of himself than the good of the country'.
He has a reputation for cracking down on corruption. He had been charged along with Hillary Clinton (then Hillary Rodham), a lawyer, on the House Justice Committee during the Watergate indictment.
As a US Attorney for Massachusetts in the early 1980s, he led a series of anti-corruption cases before being promoted to the US Department of Justice in Washington.
He continues to be a friend of the Clintons and advocated Barack Obama against John McCain in 2008, though he later said he regretted it.
As a libertarian, he is likely to target dissatisfied Republicans and independents who share his contempt for the president and his values of anti-authoritarian government, free trade and free markets, as well as personal freedom.