Just one Republican candidate, Nikki Haley, remains to challenge former President Donald Trump for the party's nomination in the November 2024 US presidential contest to take on President Joe Biden, a Democrat who is seeking reelection.
Here are the Republican Party's two candidates:
Trump has leveraged his civil cases and indictments in four separate criminal cases - unprecedented for a former American president - to boost his popularity among Republicans and raise funds, helping to make him the Republican frontrunner with 64 per cent in the latest Reuters/Ipsos polling and victories in the first two nominating contests in Iowa and New Hampshire. He is also poised to secure Nevada's delegates.
Trump, 77, has called the indictments a political witch hunt to thwart his pursuit of a second four-year term, an assertion that the Justice Department has denied.
He also faces a legal challenge that has reached the nation's top court regarding his eligibility for the ballot following the Jan.6 attack on the US Capitol.
If elected again, Trump has vowed revenge against his perceived enemies and has adopted increasingly authoritarian language, including saying he would not be a dictator except "on day one."
He has promised other sweeping changes, including gutting the federal civil service to install loyalists and imposing tougher immigration policies such as mass deportations and ending birthright citizenship.
He has also promised to eliminate Obamacare health insurance and impose harsher curbs on trade with China.
A former South Carolina governor and Trump's ambassador to the United Nations, Haley, 52, has emphasised her relative youth compared to Biden, 81, and Trump, as well as her background as the daughter of Indian immigrants.
She had gained a reputation in the Republican Party as a solid conservative who has the ability to address issues of gender and race in a more credible fashion than many of her peers.
But Trump has increasingly targeted her, including racist attacks on her ethnicity and amplifying false claims about her eligibility for the White House despite her birth in South Carolina.
Haley, who drew 19 percent support among Republicans in the Reuters/Ipsos survey, has sharpened her attacks on Trump following New Hampshire's Jan. 23 contest and raised $1 million after Trump threatened her donors.
She has also pitched herself as a stalwart defender of American interests abroad, citing Trump's praise of dictators, and ramped up her argument that Trump is too chaotic and divisive to be effective.
She has suggested she will stay in the race past the Feb. 24 primary in her home state, where opinion polls show she trails Trump.
