Cassidy Was Beaten by Trump, Then Finished Off by the Rules

Bill Cassidy did not lose like a normal incumbent. He lost like a warning.

On Saturday, May 16, 2026, Louisiana Republicans pushed a two-term U.S. senator into third place in his own primary: Rep. Julia Letlow led with 178,406 votes, or 45%, state Treasurer John Fleming took 111,840 votes, or 28%, and Cassidy finished with 98,030 votes, or 25%, according to WWNO’s posted results². Letlow and Fleming now head to a June 27 runoff for the Republican Senate nomination, a contest that will likely decide the seat in a state AP describes as strongly Republican AP reported¹.

I think the cleanest answer is this: Trump made Cassidy beatable, and Louisiana’s new rules made his escape route too narrow. If the question is why Cassidy collapsed to 25% as a sitting Republican senator, the answer is Trump-era party discipline. If the question is why he failed to grab the second runoff slot by 13,810 votes, the rules matter a lot more.

Start with the political injury. Cassidy’s original sin, in today’s Republican Party, was his vote on February 13, 2021, to convict Donald Trump in the Senate impeachment trial after Jan. 6, a vote recorded in the official U.S. Senate roll call⁹. That vote never stopped being live ammunition. AP reported that Letlow, who had Trump’s endorsement, said Cassidy’s impeachment vote showed he had turned his back on Louisiana voters, while Trump celebrated Cassidy’s defeat by tying it directly to impeachment AP reported¹. This was not a subtle subtext. It was the plot.

That is why I resist the idea that Cassidy was mainly a victim of machinery. Incumbency advantage, the built-in edge that officeholders get from name recognition, fundraising, constituent work and political relationships, should have mattered here. Cassidy had plenty of money behind him: AP reported that his campaign was expected to spend about $9.6 million on advertising through May 16, while a pro-Cassidy super PAC was on track for $12.3 million; Letlow’s campaign spent roughly $3.9 million, her allied super PAC about $6 million, and Fleming’s campaign about $1.5 million AP reported¹. Money did not save him because the attack went to identity, not awareness. Republican voters knew who Cassidy was. That was the problem.

The polling before Election Day pointed in the same direction. A February survey by JMC Analytics, commissioned by Fleming’s campaign, found Fleming at 26%, Letlow at 25% and Cassidy at 22% among likely Republican primary voters; the same release said Cassidy was at only 20% among registered Republicans, behind both Fleming and Letlow JMC Analytics reported⁸. I would treat any campaign poll with care, especially one released by a rival, but the final result validated its central warning: Cassidy’s problem was not that voters forgot him. It was that the GOP electorate had already moved away from him.

Then come the rules. Louisiana’s traditional “jungle primary” put all candidates, regardless of party, on the same first-round ballot and let all voters participate. A candidate who cleared 50% could win outright. The new closed-party primary system, adopted for selected offices beginning in 2026, changed that for races including U.S. Senate: Democratic and Republican candidates now run in separate party primaries, registered party voters get their party’s ballot, and No Party voters can choose either the Democratic or Republican primary ballot the Louisiana Secretary of State explains⁵. The Public Affairs Research Council of Louisiana said the closed system applies to U.S. Senate, U.S. House, the Louisiana Supreme Court, the Public Service Commission and the state Board of Elementary and Secondary Education, while other races continue under the open system PAR wrote⁷.

That change was not cosmetic. PAR estimated that No Party voters made up 27% of Louisiana’s electorate and had to choose a party ballot, while more than 25,000 voters registered with parties other than Democratic or Republican could not vote in closed-party primaries at all PAR wrote⁷. Axios also reported in January that the state’s dissolved Independent Party moved roughly 150,000 voters into the unaffiliated category ahead of the new primary system Axios reported¹⁰. For a conventional Republican favorite, that might be a detail. For Cassidy, it was existential.

Cassidy’s own campaign behavior tells us why. Facing a primary electorate dominated by Trump loyalists, he spent weeks urging Democrats to switch to No Party and urging No Party voters to request Republican ballots so they could vote for him, according to WWNO³. That is a strange place for a Republican incumbent to find himself. It is also the best evidence for the mixed explanation: Cassidy needed non-core Republican voters because core Republican voters were hostile, and the new system made those non-core voters harder to reach.

The election was also tangled in a broader mess. Redistricting, the redrawing of political district lines, did not directly alter the statewide Senate map, because there is no Senate district map. But it did shape the May 16 environment because Louisiana’s U.S. House primaries were suspended after a Supreme Court decision affecting congressional maps, and WWNO reported that more than 40,000 absentee ballots had already been cast for those House races when Gov. Jeff Landry announced the votes would not be counted WWNO reported⁴. WWNO also documented complaints about ballot irregularities, voters unable to vote in the U.S. Senate primary and No Party voters being required to sign affidavits WWNO reported⁴. The Secretary of State’s office warned before the election that turnout percentages would not be immediately available because parish registrars needed up to two weeks to process which ballot choices No Party voters made under the new closed-primary system the office said⁶.

That last point is important because the best version of the rules explanation is not hand-waving. Cassidy missed Fleming by 13,810 votes, based on the WWNO totals, and that is small enough that No Party turnout, ballot-selection friction, minor-party exclusion and voter confusion could plausibly have determined whether he made the runoff WWNO reported². I do not dismiss that. A voter who is legally eligible but confused is not a neutral abstraction. A voter who once saw all candidates on one ballot but now must choose a partisan ballot is being asked to clear a new hurdle.

But the rules explanation becomes too large when it tries to explain the whole result. Cassidy did not need a tweak. He needed rescue. Nearly three-quarters of Republican primary voters chose someone else, and both candidates who beat him ran as more acceptable vehicles for a party still organized around Trump. Letlow had Trump’s endorsement; Fleming, a former House member and Trump administration official, also ran to Cassidy’s right in a race AP framed as part of Trump’s effort to punish Republicans who crossed him AP reported¹.

There were other candidate-specific wounds. Cassidy, a physician and chair of the Senate Health, Education, Labor and Pensions Committee, had also antagonized Robert F. Kennedy Jr.’s “MAHA” movement after clashing with Kennedy-aligned health politics; Axios reported that Kennedy supporters targeted him after he helped derail Casey Means’ surgeon general nomination Axios reported¹¹. That probably deepened the sense that Cassidy was an institutional Republican in an anti-institutional party. But it looks secondary to the impeachment vote because Trump’s grievance supplied the broad, simple loyalty test.

So my verdict is not that the rules were a footnote. They were the blade’s edge. Louisiana’s closed primary likely hurt Cassidy exactly where he needed help, among unaffiliated voters, crossover voters and people less likely to navigate a newly complicated process. Yet the deeper cause was that Cassidy had lost the Republican Party before the first ballot problem was reported. Trump’s endorsement effect, meaning his ability to signal which candidate counts as loyal, did not merely boost Letlow. It made Cassidy’s name a negative credential.

The evidence to watch now is precise. When Louisiana releases detailed turnout data, look at No Party ballot choices by parish, prior primary history and race, then compare them with Cassidy’s strongest areas and with past jungle-primary turnout. If those voters were missing in numbers large enough to clear 13,810 votes, the rule-change story explains why Cassidy missed the runoff. My prediction is that the data will show the new rules cost Cassidy a plausible path to second place, but not that they caused his collapse. The collapse happened earlier, when a Republican senator decided Jan. 6 was worth a conviction vote and his party decided that was unforgivable.