President Donald Trump’s campaign to suppress dissent in his own party faces its most prominent test yet as he takes aim at Rep. Thomas Massie in Kentucky on Tuesday, while GOP candidates across the country look to leverage his endorsement in key primaries.

So far, Trump’s push to defeat Republicans who have crossed him has succeeded in other May primaries, ousting several Indiana state lawmakers and ending Sen. Bill Cassidy’s congressional career Saturday in Louisiana.

But it’s Massie who has drawn the most attention from Trump amid repeated clashes across multiple issues, which prompted Trump’s political operation to pour resources into the campaign. Massie’s primary against Trump-backed former Navy SEAL Ed Gallrein has drawn more ad spending than any House primary in U.S. history, according to the ad-tracking firm AdImpact.

That primary is the most bitterly contested in a slate of elections across six states Tuesday: Alabama, Georgia, Idaho, Kentucky, Oregon and Pennsylvania.

Loyalty to Trump is top of mind in other races, too, as Republicans choose nominees for competitive statewide races like the important gubernatorial and Senate primaries in Georgia. The winner in the Georgia Senate contest will face Democratic Sen. Jon Ossoff in one of the most critical races of the midterm elections.

Meanwhile, voters are starting to shape the battle for control of the House in a major way, choosing nominees for battleground races that will help decide the majority in the fall, as well as in safe seats where winners of tough primaries will be on glide paths to join Congress in 2027.

Here are the major races to watch.

Trump tests

Trump has endorsed three dozen candidates for federal office or in governor’s races with primaries Tuesday, but Massie’s race sits center stage.

Massie went to Washington as a “tea party” Republican in 2012 and has long been deeply skeptical of government spending and foreign entanglements. That has made him a thorn in Trump’s side during both of his terms in the White House, most recently on issues including the Iran war, the push to release files related to the late convicted sex offender Jeffrey Epstein and Trump’s signature tax and spending package last year.

Trump and key allies have mobilized a massive effort to boost Gallrein. Nearly $33 million has been spent on ads, largely from super PACs supporting both candidates, as well as pro-Israel groups opposing Massie.

Trump’s endorsement will be put to the test across the primaries Tuesday, and in some cases, his preferred candidates are still expected to be forced into primary runoffs.

They include his pick in Georgia’s gubernatorial primary, in which he has endorsed Lt. Gov. Burt Jones in the race to replace term-limited GOP Gov. Brian Kemp. Billionaire health executive Rick Jackson has swamped the Georgia airwaves in the race, which also includes Secretary of State Brad Raffensperger, who clashed with Trump after the 2020 election, and state Attorney General Chris Carr.

The crowded primary makes it unlikely that any one candidate will win a majority of the vote, so the top two vote-getters would advance to a June 16 runoff.

Former Atlanta Mayor Keisha Lance Bottoms could also be forced into a runoff for the Democratic nomination, since that primary also features multiple candidates, including former state Sen. Jason Esteves, former state Labor Commissioner and DeKalb County CEO Michael Thurmond and former Lt. Gov. Geoff Duncan, who served as a Republican but later switched parties.

Trump has also backed Rep. Barry Moore in the Alabama race to succeed GOP Sen. Tommy Tuberville, who is running for governor with Trump’s endorsement. Tuberville is expected to glide through his primary, and he could face a rematch against former Sen. Doug Jones, whom he defeated in a 2020 Senate race, if Jones wins the Democratic nomination.

Moore faces a Republican Senate field including state Attorney General Steve Marshall, former Navy SEAL Jared Hudson and businessman Rodney Walker. There will be a June 16 runoff if no candidate gets majority support Tuesday.

Trump did help settle the Kentucky GOP Senate primary when he backed Rep. Andy Barr this month in the race to replace retiring Sen. Mitch McConnell. One of Barr’s top opponents, businessman Nate Morris, ended his campaign after he accepted an ambassadorship from Trump.

Former state Attorney General Daniel Cameron is still in the race, though he had been trailing Barr and Morris in fundraising.

Trump has endorsed in other races, backing every House Republican incumbent on the ballot Tuesday except one, Brian Fitzpatrick of Pennsylvania, who is unopposed in his primary and has kept some distance from Trump in his purple district.

In open deep-red seats, Trump has also endorsed former Tennessee Health Commissioner Ralph Alvarado in the crowded Republican primary to succeed Barr in Kentucky’s 6th District, Jim Kingston’s bid for the Georgia 1st District seat his father once held and state Rep. Houston Gaines in Georgia’s 10th District.

Party identities on the line

Other primaries Tuesday ask both Republicans and Democrats to choose between distinctly different standard bearers for their parties.

In the hotly contested Georgia GOP Senate primary to take on Ossoff, two lawmakers — Reps. Mike Collins and Buddy Carter — have pitched themselves as staunch Trump allies. The other top candidate, former college football coach Derek Dooley, has sought Trump’s endorsement, but he has also pitched a “different kind of leadership” in Washington, calling for reforms like congressional term limits and a ban on lawmaker stock trading.

Dooley also has the backing of Kemp, the governor, who clashed with Trump over the 2020 election but handily defeated a Trump-backed primary challenger in 2022. The race will also be a key test of Kemp’s sway in his state’s Republican Party as his governorship ends and he potentially considers running for president in 2028.

A fight for the soul of the GOP is also playing out in the crowded race for Georgia secretary of state to replace Raffensperger.

The Republican primary features Gabriel Sterling, the former chief operating officer for the secretary of state’s office, who was the public face of the state’s defense of the 2020 election; former state Rep. Vernon Jones, a former Democrat who has repeated Trump’s false claims of election fraud in 2020; state Rep. Tim Fleming, Kemp’s former chief of staff; Air Force veteran Kelvin King, who ran unsuccessfully for the Senate in 2022; and former Georgia Libertarian Party Chairman Ted Metz.

Democrats also face stark choices in a handful of important primaries, both in battlegrounds and in safe blue districts.

Pennsylvania’s 7th District is expected to host one of the most competitive battleground House races this fall, but Democrats need to decide a crowded primary first, one filled with a handful of prominent candidates with different theories of the case.

Bob Brooks, a firefighters union head backed by both Pennsylvania Gov. Josh Shapiro and Sen. Bernie Sanders, I-Vt., is hammering an economic message and pitching himself as the kind of “working-class candidate” who can tap into voters’ frustration. Meanwhile, former federal prosecutor Ryan Crosswell is trying to frame himself as the solution to a “lawless” administration.

Former Northampton County Executive Lamont McClure and former Senate aide Carol Obando-Derstine are also running — and McClure has received a significant, last-minute flurry of supportive advertising spending from a group with ties to Republicans.

Then there are two safe Democratic districts with crowded primary fields, one in Pennsylvania and one in Georgia.

Pennsylvania’s 3rd District, a deep-blue seat in Philadelphia being vacated by the retiring Rep. Dwight Evans, is arguably the next front in the battle over the direction of the Democratic Party between progressives and more traditionalist candidates.

There, former state party chairman Sharif Street is running with the backing of Philadelphia Mayor Cherelle Parker and the city Democratic Party, while state Rep. Chris Rabb has been endorsed by prominent progressives like Rep. Alexandria Ocasio-Cortez, D-N.Y.

And Georgia’s 13th District, left vacant by the death of Democratic Rep. David Scott, features another crowded race in a deep-blue seat in the Atlanta suburbs, with candidates from the state Legislature, local government and a former reality TV show star backed by Fulton County District Attorney Fani Willis.

Battle for the House takes shape

Tuesday’s primary will solidify the matchup in Pennsylvania’s governor’s race, which has effectively been set for months since both Shapiro, the Democratic governor, and Republican state Treasurer Stacy Garrity are running unopposed. Trump has also endorsed Garrity’s campaign.

Shapiro’s bid for a second term will be a key race to watch since Pennsylvania is a perennial battleground, but it could also be a test of his political strength as he weighs a run for president in 2028.

Along with the 7th District, Tuesday’s primaries will set the matchups in three other competitive House races in Pennsylvania.

Scranton Mayor Paige Cognetti is running unopposed in the Democratic primary in the 8th District, where she’ll take on Republican Rep. Rob Bresnahan, who is also running unopposed. And Democratic former TV news anchor Janelle Stelson is expected to face little opposition on her path to a rematch with GOP Rep. Scott Perry in the 10th District.

Democrats also have a primary in the 1st District to decide who will take on Fitzpatrick, a perennial battleground target with an undefeated electoral record in suburban Philadelphia. The top fundraiser in the Democratic primary is Shapiro-endorsed Bucks County Commissioner Bob Harvie, and he faces a handful of opponents.

Another race on the edge of the House battleground is Oregon’s 5th District, where Deschutes County Commissioner Patti Adair and former Republican legislative aide Jonathan Lockwood are competing to face Democratic Rep. Janelle Bynum.

Other races to watch

Georgia voters will also cast their ballots in two competitive state Supreme Court races, as well as a third in which the incumbent is running unopposed.

The ideological balance of the court isn’t up for grabs in Tuesday’s technically nonpartisan races. But both justices up for re-election were appointed by a Republican governor, and their challengers are backed by prominent Democrats.

Voters will also set matchups in a handful of other statewide races, though they aren’t expected to be as competitive in November.

In Oregon, Republicans will pick contenders to take on Gov. Tina Kotek and Sen. Jeff Merkley. Kotek’s first race in 2022 was closer than usual in a state that hasn’t elected a Republican governor since 1982, because a well-known, longtime former Democratic state lawmaker ran as an independent. This year, the top candidates on the GOP side include state Sen. Christine Drazan, the GOP nominee who lost to Kotek in 2022; former professional basketball player Chris Dudley, the 2010 nominee for governor; and state Rep. Ed Diehl.

In Kentucky, a crowded group of Democratic Senate hopefuls includes Navy veteran Amy McGrath and former state Rep. Charles Booker.

In Idaho, GOP Sen. Jim Risch and GOP Gov. Brad Little are running for re-election. Both have Trump’s endorsement, with Little earning his support after having defeated a Trump-backed candidate in his 2022 primary.

Republicans are expected to win both Idaho races in November, though there is an independent candidate in the Senate race, former state Rep. Todd Achilles, a former Democrat. Achilles is one of multiple independents running for the Senate in red states.