Sen. Bill Cassidy failed to finish in the top two spots in Louisiana's Republican Senate primary on Saturday, AP projects. The race now goes to a June 27 runoff between Rep. Julia Letlow and state Treasurer John Fleming.Why it matters: It's a win for President Trump, who backed Letlow and urged voters to oust Cassidy, whom he's described as "very disloyal." Driving the news: Cassidy ran afoul of Trump when he voted more to convict the president during his Senate impeachment trial over the Jan. 6, 2021, riot at the U.S. Capitol. Trump was acquitted, but he's sought retribution against Republicans who supported the impeachment effort. Between the lines: Cassidy also helped torpedo Casey Means' nomination for surgeon general, a move that drew the ire of Health Secretary Robert F. Kennedy Jr. and the MAHA movement. Means, a health influencer, is a close Kennedy ally and a major figure in the MAHA movement. She is also the sister of Calley Means, a top Kennedy adviser.Kennedy and his supporters view Cassidy, a physician-turned-senator who chairs the Senate HELP Committee, as an avatar for the medical establishment they're determined to upend, as Axios' Alex Isenstadt wrote.Zoom in: Saturday marked the first time in more than 50 years that Louisiana used a closed-primary system to choose its U.S. senator, a change widely viewed as putting Cassidy at a disadvantage. In his previous primary victories, Cassidy's main opposition came from Democrats. Trump endorsed Letlow, a U.S. House member from the northeastern part of the state, in January. Fleming cast himself as a Trump and MAGA ally, despite not having the president's endorsement.