Incumbent Bill Cassidy (R), John Fleming (R), Julia Letlow (R), and Mark Spencer (R) are running in the Republican Party primary for U.S. Senate in Louisiana on May 16, 2026. Three candidates — Cassidy, Fleming, and Letlow — lead in fundraising and polling.

President Donald Trump (R) and Gov. Jeff Landry (R) endorsed Letlow. According to Axios' Alex Isenstadt, "Cassidy — who voted to convict Trump over his role in instigating the Jan. 6 Capitol riot — is the only Republican senator Trump's team is targeting for defeat this primary season." WBRZ's Kelly P. Kissel wrote, "Gov. Jeff Landry, who is not on the ballot, criticized Cassidy on X, formerly known as Twitter, saying the two-term senator had blocked an effort to add a conservative judge to the federal court in Baton Rouge. Cassidy noted that the Baton Rouge-based district hasn't had a vacancy since Cassidy went to the Senate in 2015."

Cassidy was first elected to the U.S. Senate in 2014. Cassidy earned his bachelor's degree and medical degree from Louisiana State University. He worked in charity hospitals and co-founded the Greater Baton Rouge Community Clinic. Cassidy was a state senator from 2006 to 2008. He represented Louisiana's 6th Congressional District in the U.S. House from 2009 until his election to the U.S. Senate.

Cassidy said, "The people of our state want safer streets, they want to be healthier, they want to have more money in their pocket. I have delivered that working with President Trump, over and over again. That’s what the race should be decided on." In an interview with KTBS, Cassidy described himself as "a conservative who's pro-life, pro-Second Amendment, pro-oil and gas, who's delivered for Louisiana."

As of the 2026 election, Fleming is the Louisiana State Treasurer. Fleming earned his bachelor's degree and medical degree from the University of Mississippi. He served in the U.S. Navy and worked as a physician and business owner. He represented Louisiana's 4th Congressional District in the U.S. House from 2009 to 2017 and was Trump's deputy chief of staff at the end of Trump's first term.

Fleming told Louisiana First News' André Moreau that he has more experience than the other candidates: "I am a family physician ... Also I opened up a number of businesses that operate. ... I served eight years in the House of Representatives, I worked four years in the Trump administration. ... And then I've been your state treasurer for the last two years, so I'm bringing all that experience to this job." Fleming's campaign website said, "Now, John Fleming is running for the U.S. Senate to take that same conservative leadership to Washington — defending our values, securing our borders, protecting Louisiana jobs, and standing shoulder-to-shoulder with President Trump to put America First."

As of the 2026 election, Letlow represented Louisiana's 5th Congressional District. Letlow earned her bachelor's and master's degrees from the University of Louisiana Monroe and her doctorate from the University of South Florida. She worked as a university professor and administrator before her election to the U.S. House in 2021.

Letlow said she is running "to ensure the nation we leave our children is safer and stronger. Louisiana deserves a conservative Senator who will not waver. I am honored to have President Trump’s endorsement and trust." Letlow said in a campaign advertisement, "I have fought alongside President Trump to put America first — standing up for our parents, securing our borders, supporting law enforcement, rooting out waste, fraud, and abuse that drives up inflation, and fighting to fix an education system too focused on woke ideology instead of teaching."

Louisiana will use closed party primaries for some offices in 2026, including the U.S. Senate, meaning Democrats and Republicans will select nominees for the general election. Previously, Louisiana used the majority-vote primary, commonly called a jungle primary. In that system, all candidates appeared on the same ballot and the top-two finishers advanced to the general election regardless of their party. A candidate who earned a simple majority of the vote in the primary won the election outright.