The victory, projected by several US media outlets including AP, CNN and CBS, is the first step of a process to choose the Republican candidate for the November election.
Florida Governor Ron DeSantis and former UN Ambassador Nikki Haley are competing for second place.
Trump's margin was not immediately clear.
Trump has long been considered the near-certain Republican nominee as he has held a commanding lead for months over the remaining Republican contenders.
A compilation of national polling from the RealClearPolitics website has Trump leading all other candidates with 51% support among Republican voters.
US President Joe Biden, meanwhile, is largely running unopposed for the Democratic nomination, leaving him a wide-open path to securing his party’s nomination.
Whichever candidate garners the majority of their party's delegates will be considered the presumptive nominee heading into their national convention.
Voters will take to polling stations across the country for Election Day on Nov. 5.
AzVision.az
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