Former Massachusetts Gov. Mitt Romney is projected to win his primary runoff in the race to replace retiring Utah Republican Sen. Orrin Hatch, marking the latest in a string of victories by Trump-backed candidates on Tuesday.
In all, seven states were holding primaries or runoffs across the country on Tuesday, with the Utah contest among the highest-profile.
As victories by Trump-backed candidates piled up, the president weighed in on Twitter, calling Tuesday a "big night."
"The Democrats are in Turmoil!" Trump wrote. "Open Borders and unchecked Crime a certain way to lose elections. Republicans are for Strong Borders, NO Crime! A BIG NIGHT!"
The president also retweeted an image of himself surfing a massive red wave, while a panicked donkey on top of a small blue puddle mutters repeatedly, "Blue wave!"
Romney beat back a challenge from little-known state Rep. Mike Kennedy, who emphasized his local experience in order to draw a contrast with the former GOP presidential candidate.
Romney and Kennedy were competing in the runoff because neither was able to secure at least 60 percent of delegates' support at the state GOP convention earlier this year.
Romney is set to face Democrat Jenny Wilson, a county councilwoman, in the general election in the deep-red state.
Romney, who lambasted Trump as a "fraud" and a "con man" in the run-up to the 2016 presidential election, has softened his tone substantially since then. Trump has endorsed Romney in the race, saying in February that Romney has his "full support and endorsement."
"I think President Trump will be re-nominated by my party easily, and I think he'll be reelected solidly," Romney, whom Trump briefly considered as a potential secretary of state, said in June.
In a weekend op-ed published in The Salt Lake Tribune, Romney wrote that the Trump administration's policies have exceeded his expectations, but he pledged to "continue to speak out when the president says or does something which is divisive, racist, sexist, anti-immigrant, dishonest or destructive to democratic institutions."
The unusual on-again, off-again relationship between Trump and Romney led the Boston Globe this week to call him "the face of Trump's enablers or enemies. Or both."
Voters also headed to the polls in New York, Maryland, Colorado, Mississippi, Oklahoma and South Carolina on Tuesday.
Buoyed by a risky, full-throated endorsement by President Trump, South Carolina Gov. Henry McMaster was projected to win Tuesday's Republican gubernatorial runoff election.
The White House went all-in to support McMaster, with Trump and Vice President Mike Pence campaigning on his behalf in recent days.
In New York, another Trump-backed candidate, Rep. Dan Donovan, prevailed over the comeback candidacy of Michael Grimm.
Grimm, who had been convicted for tax fraud, was considered a liability in the district in November for Republicans.
And in a shocking result, 10-term Democratic Rep. Joe Crowley, a fierce Trump critic and chairman of the influential House Democratic Caucus, was summarily unseated by far-left 28-year-old candidate Alexandria Ocasio-Cortez.
In Maryland, incumbent Sen. Ben Cardin won the Democratic nomination for his bid to earn a third term, beating far-left convicted leaker Chelsea Manning and six others.
Fox News' Alex Pappas, Kaitlyn Schallhorn and The Associated Press contributed to this report.