Trump endorsed Republican Representative Julia Letlow in an unusual attempt to unseat an incumbent senator, targeting Cassidy over his vote to convict Trump during his 2021 impeachment trial following the Jan. 6 attack on the U.S. Capitol.

In social media posts hours before voting began, Trump described Cassidy as “a disloyal disaster” and “a terrible guy,” while predicting the senator would be “CLOBBERED” in the primary. Trump praised Letlow as “a winner” who would remain loyal to his political agenda.

The contest also includes Louisiana State Treasurer John Fleming, a former congressman and longtime Trump ally. Under Louisiana election rules, a runoff election will be held June 27 if no candidate secures more than 50% of the vote.

The race is widely viewed as a referendum on Trump’s dominance within the Republican Party ahead of the 2026 midterm elections, particularly among conservatives who have challenged him on impeachment, public health policy or institutional governance.

Cassidy, a physician and chair of the Senate health committee, has faced sustained criticism from Trump-aligned Republicans over both his impeachment vote and his cautious stance toward Health Secretary Robert F. Kennedy Jr., whose confirmation Cassidy ultimately supported despite expressing concern over Kennedy’s vaccine views.

Trump recently blamed Cassidy for undermining the nomination of surgeon general candidate Casey Means after the senator publicly defended hepatitis B vaccinations for newborns, a position at odds with some vaccine skeptics allied with Kennedy.

Despite trailing Trump-backed enthusiasm in the state, Cassidy mounted an expensive and increasingly aggressive campaign in the final weeks of the race. According to advertising tracker AdImpact, Cassidy’s campaign and affiliated super PAC Louisiana Freedom Fund were projected to spend more than $21 million combined on advertising through May 16.

By comparison, Letlow’s campaign and the pro-Letlow Accountability Project super PAC were projected to spend roughly $10 million combined. Fleming’s campaign spending totaled approximately $1.5 million.
Cassidy and allied groups sought to portray Letlow as insufficiently conservative by highlighting her previous support for diversity, equity and inclusion initiatives during her tenure as a university administrator before entering Congress.

Political analysts said the contest had tightened in recent months despite Trump’s dominance in Louisiana, a state he carried comfortably in three presidential elections.

The election also unfolded amid voter confusion triggered by Louisiana’s delayed congressional primaries following a recent U.S. Supreme Court ruling affecting enforcement of portions of the Voting Rights Act tied to congressional district maps. State officials postponed House primaries to redraw district boundaries, while the Senate primary proceeded as scheduled.

Analysts said the scheduling changes could affect turnout patterns, particularly among less politically engaged voters.

Letlow entered the race only after securing Trump’s endorsement in January, despite earlier speculation about a possible candidacy. Her political rise followed the death of her husband, Luke Letlow, who died from COVID-19 complications in 2020 shortly after being elected to Congress but before taking office. She later won the seat in a special election and retained it in subsequent elections.