Primaries across four states Tuesday will shape one of the most closely watched Senate races of the year in Michigan, and see one “Squad” member defend her seat from a primary challenger at St. Louis.

In Michigan, voters will go to the polls to choose the nominees for what is expected to be one of a handful of “tossup” Senate races in 2024.

The Democrats are expected to nominate Congresswoman Elissa Slotkin and the Republicans are expected to nominate a former congressman, Mike Rogers, for the general election race to replace a retiring four-term senator, Debbie Stabenow.

Ms. Slotkin has proved electorally resilient in the state, winning her competitive House district, Michigan’s Seventh, with about 52 percent of the vote in 2022.

Mr. Rogers is returning to electoral politics in 2024. He had previously represented Michigan’s Eighth between 2001 and 2015; it was a safe Republican seat during his tenure.

Democrats are hoping to hold onto the seat while Republicans are attempting to take one of Michigan’s Senate seats for the first time in 24 years.

In the primaries, Ms. Slotkin is the favorite against her lone challenger, a Detroit business owner, Hill Harper. On the Republican side, Mr. Rogers faces a field of four candidates, including Congressman Justin Amash, who is best known for voting to impeach President Trump before leaving the GOP to become a Libertarian.

Mr. Amash, the son of Palestinian and Syrian immigrants, is also campaigning for the support of Michigan’s considerable Arab American population, hoping to capture the votes of voters with negative views of both parties. While most of the Republican Party has lined up in support of Mr. Rogers, Senator Paul has endorsed Mr. Amash.

So far, public polling for the general election has suggested that Ms. Slotkin would enjoy an advantage over Mr. Rogers at the beginning of the race.

A recent Fox News survey conducted with Beacon Research and Shaw and Company Research found Ms. Slotkin with a 5-point lead ahead of the primaries. While the margin differs, all public polling so far has shown Ms. Slotkin in the lead.

The state is also holding its House primaries on Tuesday and is expected to see a few competitive House races in November, including in its Third, Eighth, and 10th districts.

Aside from the competition in Michigan, the most high-profile primary is in Missouri, where Congresswoman Cori Bush, a member of Representative Alexandria Ocasio-Cortez’s self branded Squad, is defending her St. Louis seat against a more conservative Democratic challenger, Wesley Bell.

Mr. Bell, who enjoys a substantial cash advantage over Ms. Bush and leads slightly in most polls, has attempted to frame his candidacy around his record as a prosecutor in contrast to Ms. Bush’s populist activism.  

The race has drawn national attention because it is the second prominent Democratic House race where pro-Israel lobbying groups have backed primary challengers against sitting representatives. 

Earlier this year, pro-Israel groups successfully backed the challenge to Congressman Jamaal Bowman, a Squad member, by the Westchester County executive, George Latimer, in New York’s 16th District.

In the New York race, the American Israel Public Affairs Committee broke records for spending in a congressional primary, $14.5 million, in its attempt to unseat Mr. Bowman. 

So far in St. Louis, Aipac has spent more than $8.4 million in its effort to unseat Ms. Bush. Both Ms. Bush and Mr. Bowman have been vocal critics of Israel’s response to the October 7 terrorist attack by Hamas.

The primary for Missouri secretary of state will also be on the ballot Tuesday. This year the race has drawn particular attention due to one candidate, a social media personality, Valentina Gomez, who is running in a crowded Republican field.

The Colombian-born Ms. Gomez has drawn attention for her statements on LGBTQ issues, cutting promotional videos in which books concerning LGBTQ themes are burned, telling voters “‘don’t be weak and gay,” and saying of one female Olympic athlete who has been accused of secretly being a man: “These f—-ts don’t belong in women’s sports.”

There will also be primaries held in both Kansas and Washington. In Washington, the Third District is expected to be competitive in November.