Trump endorsement rocks Louisiana Senate race as Letlow jump in

Three days after President Donald Trump exploded a political bomb in Louisiana's Senate race by endorsing Republican Rep. Julia Letlow over incumbent GOP Sen. Bill Cassidy, Letlow announced her campaign.

Letlow declared her candidacy at a closed-door business breakfast in Baton Rouge, Louisiana, Tuesday morning, according to Republican sources.

Trump's support of Letlow, who was elected in 2021 after her husband Luke died from COVID shortly before taking office in the House, is a serious setback for Cassidy, a physician and chair of the powerful Senate Health committee who is running for a third six-year term in the solidly red state.

And it's a major political headache for Senate Majority Leader John Thune, who is backing Cassidy and teamed up with the senator last week in Louisiana.

Trump upended an already crowded GOP Senate primary in Louisiana on Saturday night, with a social media post making it clear that if the 44-year-old Letlow launched a Senate campaign, she'd have his backing.

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"Should she decide to enter this RACE," Trump wrote on social media, "Julia Letlow has my Complete and Total Endorsement. RUN, JULIA, RUN!!!"

Letlow hinted at launching a Senate run following Trump's post on X, writing, "My mission is clear: to ensure the nation our children inherit is safer and stronger. This United States Senate seat belongs to the people of Louisiana, because we deserve conservative leadership that will not waver."

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There's been speculation for months that Letlow was mulling a Senate bid and a Republican source confirmed to Fox News that the congresswoman, who represents a district that covers parts of central and northeastern Louisiana, had indicated that she wouldn't challenge Cassidy without Trump's backing.

A separate Republican source confirmed to Fox News that Trump had reached out to Thune on Friday to give the Senate's top Republican a heads-up on the Letlow endorsement.

Thune continues to support Cassidy, who was also previously endorsed by the National Republican Senatorial Committee, which is the Senate GOP's campaign arm.

But the deep-pocketed Senate Leadership Fund (SLF), which is the top super PAC supporting Senate Republicans and is aligned with Thune, is staying neutral in Louisiana.

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"The mission of the Senate Leadership Fund is to preserve and expand the Republican Senate majority. Anything that distracts from our efforts to beat Democrats in November is unhelpful," SLF Executive Director Alex Latchum wrote in a statement to Fox News Digital.

Word that SLF was staying out of the GOP primary in Louisiana was first reported by Punchbowl News.

The 68-year-old Cassidy is staying in the race.

"I’m proudly running for re-election as a principled conservative who gets things done for the people of Louisiana," Cassidy wrote on social media following Trump's bombshell. "If Congresswoman Letlow decides to run, I am confident I will win."

Cassidy had nearly $10 million in his campaign coffers at the end of October, after his last fundraising filing, with Letlow holding nearly $2.3 million cash on hand. But a burst of campaign cash will likely flow Letlow's now that she's launched a Senate campaign.

The senator — who voted to convict Trump in the Senate impeachment trial following the Jan. 6, 2021 attack on the U.S. Capitol by Trump supporters aiming to upend congressional certification of former President Joe Biden's 2020 election victory — early last year supported Trump's controversial cabinet nominees, including Robert F. Kennedy, Jr. for Health secretary.

But the Make America Healthy Again (MAHA) PAC, which has close ties to Kennedy, announced on Sunday that it would financially support Letlow.

Louisiana State Treasurer John Fleming, a former congressman who served in Trump's first administration, is also challenging Cassidy.

"A recent poll shows our campaign expanding our lead on Bill Cassidy, while Cassidy's numbers continue to drop," Fleming noted on social media two days after Trump's endorsement of Letlow.

State Sen. Blake Miguez and state Rep. Julie Emerson are also running for the GOP Senate nomination, and former Rep. Garrett Graves is mulling a bid.

Trump's endorsement of Letlow increases speculation on whether he'll take sides in the combustible and competitive GOP Senate primary in Texas ahead of the early March primary.

Longtime Sen. John Cornyn is facing primary challenges from two Trump allies, Texas Attorney General Ken Paxton and Rep. Wesley Hunt.

Thune speculated last week that Trump wouldn't make an endorsement in the Texas GOP showdown.