Iran gridlock and middling China trips aside, President Donald Trump is having a pretty good month. Three May elections tested his grip on the Republican Party — and his candidates cleaned up.

In Indiana, five Trump-backed challengers defeated Republican state senators who opposed the president’s efforts to redraw state electoral maps.

In Louisiana, Sen. Bill Cassidy — who angered Trump by voting to convict him in his second impeachment trial, after January 6 — lost decisively to a MAGA candidate backed by the president.

In Kentucky, meanwhile, Trump waged an aggressive campaign against House Republican Thomas Massie, who championed the release of the Epstein files and criticized the Iran war. The eight-term lawmaker was defeated last night by Ed Gallrein, a Trump surrogate and political newcomer.

Trump has cast these victories as proof his influence remains undiminished. But a New York Times/Siena poll released Tuesday found his approval rating at a second-term low of 37 percent — and his overall unpopularity is key to why Republicans run a real risk of losing Congress in the November midterm elections.

Ready for prime time. This apparent contradiction comes down, in large part, to who votes in primary elections. In a two-party system, primaries are where ideological differences within each party actually get hashed out — where, as Vox’s Matt Yglesias once put it, “nuance enters the political process.”

Yet just 1 in 5 eligible voters turn out for midterm primaries, and those voters tend to be whiter, older, wealthier, and more partisan than the electorate overall. That helps explain why ideas at the outer fringes of each party tend to take up more oxygen during primary elections.

It also helps explain how Trump-backed candidates are performing so well. Despite the president’s falling approval ratings, diehard Republicans remain loyal: Three-quarters of Republicans and Republican-leaning independent voters still approve of the job Trump’s doing, according to that New York Times/Siena poll.

Uncompetitive elections. Primaries matter even more amid the so-called “redistricting wars,” as both parties race to redraw electoral maps and squeeze out additional safe seats. Gerrymandering and political self-sorting have made general elections far less competitive since the 1970s.

Today, most members of Congress hail from safely Democratic or Republican districts: Only 18 of 435 House races are considered toss-ups, according to the Cook Political Report. In other words, most members of Congress are effectively chosen in their party’s primary election.

“The root cause of our political dysfunction is that November elections in this country are for the most part meaningless,” the political reformer Katherine Gehl told my colleague Andrew Prokop in 2022. “Most November voters are wasting their time, which is…profoundly undemocratic and unrepresentative.”

The quest to get rid of partisan primaries. Gehl is among the reformers pushing to scrap partisan primaries altogether — an effort Nevada adopted in 2022. In November of that year, the state voted to institute a nonpartisan primary, in which all candidates, regardless of party, compete in the same election. The top five candidates then go on to the general, where people vote for multiple candidates ranked by preference.

California, Washington, and Alaska also use a type of nonpartisan primary, and Maine and New York City both use ranked-choice voting for some elections. Advocates say these systems reduce polarization by forcing candidates to appeal to a wider swath of the electorate.

Would that have helped Bill Cassidy or the Indiana Republicans? It’s hard to say.

But reforming the primary would — at least in theory — insulate some independent-minded Republicans from the furor of Trump’s base.