Michigan is the only out-and-out battleground state voting on Tuesday, and its headline race is an open U.S. Senate seat that Democratic Sen. Debbie Stabenow's retirement has left up for grabs. On the Democratic side, Rep. Elissa Slotkin looks well-positioned to defeat actor Hill Harper: She's regularly polled above 50 percent in the primary contest while outraising Harper $24.1 million to $2.8 million.

Until a couple of weeks ago, the Republican primary contest looked at least somewhat more competitive. Former Rep. Mike Rogers, who retired from Congress in the 2014 cycle and had previously been critical of Trump, shifted his rhetoric and garnered the former president's endorsement in March, which along with his fundraising haul of $5.4 million has made him the favorite. Businessman Sandy Pensler, who'd self-funded almost all of his campaign's $5.0 million war chest, did seem to have the wherewithal to challenge Rogers. But on July 20, Pensler dropped out and endorsed Rogers, making the former congressman an even clearer favorite.

Now Rogers only has to contend with two other candidates, both of whom have criticized Rogers's conservative bona fides. The more notable name is former Rep. Justin Amash, who famously left the GOP to become an independent and voted to impeach Trump in 2019. In his campaign, Amash has run as a small-government critic of Rogers, whom Amash has accused of being an "establishment stooge" and part of the "deep state." Still, Amash has only raised $703,000, and while pro-Amash groups have forked out $1.7 million to boost him or attack Rogers, that's a far cry from the $5.0 million that outside groups have spent to help Rogers. Additionally, physician and pastor Sherry O'Donnell is running as an ardently pro-Trump candidate with endorsements from a number of far-right figures. But she's only brought in $434,000 and has received no outside assistance.

—Geoffrey Skelley, 538

The Republican primary in the dark-red 3rd District has gotten a fraction of the attention of Bush's contest in the 1st, but it has similarly high ideological stakes. Old-guard Republican Rep. Blaine Luetkemeyer is retiring, and it seems likely he will be replaced by a more hardline conservative, former state Sen. Bob Onder (whom Luetkemeyer also defeated in the 2008 primary en route to winning this seat in the first place). A bunch of GOP heavy hitters (Trump, the House Freedom Fund, the Club for Growth) have lined up behind Onder, who was known for his obstructionist ways in the state legislature.

Not everyone is thrilled about the prospect of Onder heading to Congress, however. Establishment-aligned super PACs have spent $4.9 million opposing Onder or supporting his main opponent, former state Sen. Kurt Schaefer, outdistancing the $3.0 million groups have spent to boost Onder or attack Schaefer. Luetkemeyer is supporting Schaefer as well, but it doesn't seem like he's catching on. Onder's campaign recently released a poll from Remington Research Group showing him leading Schaefer 34 percent to 14 percent, with five minor candidates combining for 16 percent, and 35 percent undecided. Even if we assume that poll is exaggerating Onder's support, it's unlikely that it's off by 20 whole percentage points.

—Nathaniel Rakich, 538

Perhaps no district in the country has seen more political activism in the past decade than Missouri's 1st District. In 2020, on her second try, now-Rep. Cori Bush — a progressive activist who first rose to prominence in the 2014 Ferguson protests in this district — defeated an entrenched incumbent representative in the Democratic primary in this safely blue seat, and she instantly made a name for herself as an activist legislator in Congress.

But her contrarianism — for example, she was one of just six Democrats to vote against President Joe Biden's infrastructure bill — has rubbed many the wrong way. It doesn't help, too, that the Department of Justice is investigating her for paying her husband for personal security services out of her campaign's bank account. As a result, Bush is now facing a serious primary challenge of her own from St. Louis County Prosecutor Wesley Bell.

Like Bush, Bell was first elected as a progressive in the wake of the Ferguson protests, but in this race he has inevitably become associated with the centrist and conservative donors and groups backing his campaign — most notably the American Israel Public Affairs Committee. AIPAC's super PAC has spent a whopping $8.4 million either supporting Bell or opposing Bush, who has been one of Israel's loudest critics in Congress over its conduct in the war against Hamas.

All told, pro-Bell groups have outspent pro-Bush groups $12.1 million to $2.9 million, according to OpenSecrets, and Bell's actual campaign has outraised Bush's $4.8 million to $2.9 million as well. But with all the advantages of incumbency as well as plenty of local endorsements, Bush will not be easy to defeat. A July 21-24 poll conducted by the Mellman Group/Democratic Majority for Israel gave Bell 48 percent support and Bush 42 percent, but since DMFI supports Bell and internal polls usually overestimate their preferred candidate's support, that implies the two candidates are neck-and-neck.

—Nathaniel Rakich, 538

The presidential news cycle certainly hasn't let up over the past few weeks, and you'd be forgiven if you haven't been paying much attention to downballot primary contests. But Kamala Harris's VP pick wasn't the only big political news today — it's also the busiest election day left before the big day in November.

Voters in four states hit the ballot boxes today to weigh in on which Democrats and Republicans will be on their ballots this fall, and we're tracking over a dozen key congressional, gubernatorial and other races in Missouri, Michigan, Washington and Kansas. Polls close at 8 p.m. Eastern in Missouri and most of Michigan and Kansas, so we'll expect a steady flow of results after that, until the next and last polls close in Washington state, at 11 p.m. Eastern.

It's our last primary live blog of the season, so we hope you'll join us!

—Tia Yang, 538