WASHINGTON (AP) - The exits of two leading Iowa Republican officials, Gov. Kim Reynolds and U.S. Sen. Joni Ernst, have created waves across Tuesday's state primary, sparking active nomination battles to succeed them along with a series of open positions lower on the ballot.

The victors advance to November's pivotal midterm contests, where Iowa's U.S. Senate and House races may decide control of the tightly balanced chambers. The incoming governor might also shape the 2028 presidential race, given the state's record of elevating or ending White House bids.

Two Republicans and two Democrats seek the nomination to succeed Ernst, who declared in 2025 she would skip a third term. U.S. Rep. Ashley Hinson competes against former state Sen. Jim Carlin for the GOP nod, while state Rep. Josh Turek and state Sen. Zach Wahls vie for the Democratic slot. Carlin previously ran for Iowa's other Senate seat in 2022 and captured roughly 27 percent of the primary vote against U.S. Sen. Chuck Grassley.

Reynolds likewise stated in 2025 she would not pursue another term. Candidates for the Republican nomination include state Rep. Eddie Andrews, U.S. Rep. Randy Feenstra, entrepreneur and private school co-founder Zach Lahn, former state Rep. Brad Sherman and former state administrative services director Adam Steen. President Donald Trump has backed Feenstra.

The nominee will face Democratic state Auditor Rob Sand, who runs unopposed in his primary. Sand remains Iowa's sole Democrat holding statewide elected office.

Hinson's and Feenstra's statewide bids have opened contests in the state's 2nd and 4th Congressional Districts. Feenstra's district leans heavily Republican and is unlikely to affect chamber control. Hinson's district offers more competition, though she secured reelection in 2024 with 57 percent of the vote.

In Iowa's most contested congressional districts, Republican U.S. Reps. Mariannette Miller-Meeks of the 1st District and Zach Nunn of the 3rd District both seek reelection. Miller-Meeks faces a rematch against her 2024 primary challenger, advertising executive David Pautsch, who earned about 44 percent of the vote. The Democratic side features former state Rep. Christina Bohannan, who fell just 1 percentage point short of defeating Miller-Meeks in one of 2024's tightest House races.

In the 3rd Congressional District, both Nunn and his Democratic opponent, state Sen. Sarah Trone Garriott, run unopposed in their primaries.

Trump captured roughly 54 percent of the 2024 presidential vote in both the 1st and 2nd Congressional Districts and about 52 percent in the 3rd District.

Polk, Linn and Scott counties rank as Iowa's largest population centers and influence both Republican and Democratic statewide primaries. Johnson County is fourth in size, yet as home to Iowa City and the University of Iowa it functions as a strong Democratic base and carries far less weight in Republican primaries.

Here are key facts about the election and metrics the AP Decision Team will track as votes are counted.

When do polls close?

Polls close at 8 p.m. CT, which is 9 p.m. ET.

What's on the ballot?

The Associated Press will report vote totals and name winners in contested primaries for U.S. Senate, U.S. House, governor, auditor, state Senate and state House.

Who gets to vote?

Only voters registered with a political party can take part in that party's primary. Voters may switch party affiliations at the polls on primary day.

How many voters are there?

As of May 4, Iowa had about 2.1 million registered voters, including roughly 692,000 Republicans, about 496,000 Democrats and approximately 589,000 unaffiliated voters.

How many people actually vote?

About 196,000 Republican primary votes and roughly 157,000 Democratic primary votes were cast in the 2022 U.S. Senate primaries.

How much of the vote is cast early or by absentee ballot?

About 16 percent of the Republican primary vote and about 25 percent of the Democratic primary vote in the 2022 U.S. Senate primaries arrived before primary day.

As of Friday, roughly 48,000 ballots had already been submitted for Tuesday's election, with about 30,000 in the Democratic primary and more than 18,000 in the Republican primary.

When are early and absentee votes released?

Nearly all counties release absentee-by-mail results at the start of the evening. Counties differ on when they release in-person absentee results.

How long does vote-counting usually take?

In the last contested state primary in 2022, the AP first reported results at 9:12 p.m. ET, or 12 minutes after polls closed. The final update came at 2:29 a.m. ET, with more than 99 percent of votes tallied.

When will the AP declare a winner?

The AP does not issue projections and names a winner only when no scenario remains that would let a trailing candidate close the gap. If a race stays uncalled, the AP will continue reporting newsworthy updates such as concessions or victory claims while noting that no winner has been declared and explaining the reason.

How do recounts work?

Iowa lacks an automatic recount statute, yet candidates may request and fund a recount. They avoid paying when the margin falls below 1 percent of total votes or fewer than 50 votes, whichever is greater. The AP may declare a winner in a recount-eligible race if the lead appears too large for a recount or legal challenge to alter the result.

Are we there yet?

As of Tuesday, 154 days remain until the 2026 midterm elections.

- Robert Yoon, Associated Press