In 2023, a crowded field of candidates emerged, including Trump, Florida governor Ron DeSantis, former Ambassador to the United Nations Nikki Haley, and wealth management executive Vivek Ramaswamy.

[23] At the January 15 Iowa caucuses, Trump posted a landslide victory, with DeSantis narrowly beating out Haley for second place and Ramaswamy in a distant fourth.

[28] After Trump's overwhelming victories nationwide on Super Tuesday, Haley suspended her campaign on March 6, having only won Vermont and the District of Columbia.

[30] Some Republicans expressed concerns about Trump's candidacy due to his loss in 2020, his alleged role in inciting the January 6 Capitol attack, ongoing criminal cases against him, and the results of the 2022 midterms in which several Trump-endorsed candidates lost key races;[31] many others supported him and decried the investigations as politically motivated,[32] and Trump maintained high favorability ratings among Republican voters.

[33] Trump's eligibility to appear on the ballot was challenged by some voters and political leaders in Colorado, Maine and Illinois;[34][35][36] these efforts were rejected by the Supreme Court of the United States in a unanimous decision.

[37] Trump became the presumptive nominee on March 12, with his victory in the Washington primary bringing him over the 1,215 delegate threshold needed to clinch the nomination.

[109] On March 2, businessman Perry Johnson, who had been deemed ineligible to appear on the Republican primary ballot in the 2022 Michigan gubernatorial election due to allegedly fraudulent signatures, announced his intent to run for president in 2024.

He delivered a speech the next day at the Ronald Reagan Presidential Library to publicly announce his campaign, as four other Republicans in the race had done in the last year.

[133] On August 21, the slate of candidates that officially qualified for the debate was released: Doug Burgum, Chris Christie, Ron DeSantis, Nikki Haley, Asa Hutchinson, Mike Pence, Vivek Ramaswamy, and Tim Scott.

[135] To be eligible for this debate, a candidate must have polled at least one percent, received donations from 40,000 individuals, and signed a loyalty pledge to back whoever ultimately wins the party presidential nomination.

[136] Candidates deemed eligible for the debate were Doug Burgum, Chris Christie, Ron DeSantis, Nikki Haley, Asa Hutchinson, Mike Pence, Vivek Ramaswamy and Tim Scott.

[139] On September 18, Donald Trump's campaign announced that he would be giving a speech in Detroit before striking United Auto Workers union members at the same time as the second debate in California.

[142] As of September 26, the slate of candidates that qualified for the second debate and would attend included: Ron DeSantis, Nikki Haley, Tim Scott, Vivek Ramaswamy, Mike Pence, Chris Christie, and Doug Burgum.

[144] On October 2, the Supreme Court of the United States declined to hear John Anthony Castro's case to disqualify Donald Trump from appearing on the ballot.

[153] On November 6, the RNC announced that the following candidates qualified for the third presidential debate; Donald Trump, Ron DeSantis, Nikki Haley, Vivek Ramaswamy, Chris Christie and Tim Scott.

[156] On November 20, the United States Court of Appeals for the District of Columbia Circuit reached a compromise between Trump and Chutkan, issuing a narrow gag order preventing Trump from "insulting" prosecutors, court personnel and potential witnesses, but allowing him to speak freely about outside counsel and issues relating to his presidential campaign.

[162] On December 22, CBS reported that Donald Trump was inquiring within his campaign and with his allies over the possibility of tapping Nikki Haley for his running mate.

Navarro stated that Castro, a resident of Texas who cited the 14th Amendment in the case, does not have the standing to sue Trump under Nevada law.

[211] On July 15, Trump was officially nominated at the Republican National Convention, and selected Senator JD Vance as his running mate.

On December 19, 2023, the Colorado Supreme Court ruled in Anderson v. Griswold that he was ineligible under Section 3 of the 14th Amendment due to his role in the January 6, 2021, United States Capitol attack.

[212] On February 28, a Cook County judge, Tracie Porter, ordered the removal of Trump from the ballot in Illinois, also citing Section 3 of the 14th Amendment.

[215] To be eligible for the debate, a candidate must have polled with at least 1% of voter support, received donations from 40,000 individuals, and signed a loyalty pledge to back whoever ultimately wins the party presidential nomination.

[136] Doug Burgum, Chris Christie, Ron DeSantis, Nikki Haley, Asa Hutchinson, Mike Pence, Vivek Ramaswamy, and Tim Scott all qualified for the first debate.

[222] Additionally, a scheduled sixth debate, meant to occur on January 18, 2024, in Goffstown, New Hampshire, hosted by ABC, was cancelled two days prior.

Democrats, who were in control of the Michigan legislature and governorship after the 2022 midterm elections, moved up both primaries as part of their own 2024 presidential delegate selection plan.

In contests until March 15, delegates must be awarded on a proportional basis, either by percentage of statewide vote or share of congressional districts won.

[248][249][better source needed] North Dakota, Wyoming, American Samoa, Guam, Virgin Islands, and 51 of Pennsylvania's 67 delegates are unpledged (free to vote for anyone at the convention), totaling 119.

Florida, New Jersey, Ohio, Colorado, Arizona, Nebraska, South Dakota, and Montana's delegates are strictly awarded on a plurality-take-all basis, totaling 428.

The primaries will conclude with a final vote on the nominee by a majority of delegates, at the newly elected Republican National Convention in Milwaukee, which will be held July 15–18.

[248][249][better source needed] According to the current rules of the Republican Party, no candidate can have their name placed into nomination, thereby earning television airtime at the Republican National Convention, unless he or she has received a plurality of delegates in at least five states (the rules state that "'state' or 'states' shall be taken to include American Samoa, the District of Columbia, Guam, the Northern Mariana Islands, Puerto Rico, and the Virgin Islands").