DES MOINES, Iowa (AP) — After kicking off the presidential primary season with their nominating caucuses, Iowa voters turn their attention to state offices Tuesday with several key races — including the Democratic contest to decide a challenger against longtime Republican Sen. Chuck Grassley.

Candidates also are seeking primary victories in three of Iowa's four congressional districts as well as contested legislative races.

Polls for in-person voting will be open Tuesday from 7 a.m. to 9 p.m. Early voting through absentee ballot has been available for weeks, but voters needed to postmark their ballots by Monday to have it count.

Here are some of the races to watch during the Iowa state primary:

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U.S. SENATE

Grassley, one of the best-known names in Iowa politics, hasn't lost an election since his first run for state Legislature in 1958. That's not stopping national Democrats from trying to stop his re-election bid this year.

The chairman of the Senate Judiciary Committee has been criticized for his refusal to hold confirmation hearings for President Barack Obama's Supreme Court nominee, Merrick Garland.

The leading Democratic candidate against Grassley has a fitting name: Patty Judge. The former lieutenant governor and state agriculture secretary was recruited to run by national Democrats, and she has raised more money than her three other opponents despite a late entry into the field.

Judge contends she has the experience and name recognition to take on Grassley, but Democratic activists say it could be a tough primary. Judge's main challenger, state Sen. Rob Hogg, has endorsements from most Democratic state lawmakers and two labor unions.

The Des Moines Register/Mediacom Iowa Poll released Saturday shows Judge had support from 42 percent of likely Democratic voters compared to 25 percent for Hogg. The poll, based on telephone interviews with 542 Iowa residents, has a maximum margin of error of plus or minus 4.2 percentage points.

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1ST CONGRESSIONAL DISTRICT

It's a rematch in the Democratic race to challenge Republican Rep. Rod Blum. Former state legislator Pat Murphy and former Cedar Rapids City Council member Monica Vernon faced each other and others two years ago. Murphy won but went on to lose in the general election against Blum.

Murphy and Vernon have at times taken aggressive stands during the campaign, and both claim to be the most progressive candidate. The race has received extra attention because it's seen as a serious opening for Democrats nationwide to try to take back a majority in the U.S. House.

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3RD CONGRESSIONAL DISTRICT

There are three Democratic challengers seeking to take on Rep. David Young for a district that covers southwest Iowa. The candidates — former National Guard soldier Jim Mowrer, retired financial services executive Mike Sherzan and businessman Desmund Adams — agree on most issues, including proposals to raise the minimum wage. The campaign has largely focused on who is best positioned to beat Young, a longtime Grassley aide who is seeking a second term.

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4TH CONGRESSIONAL DISTRICT

Steve King, a seven-term Republican congressman who represents northwest Iowa, is facing a primary challenge from state Sen. Rick Bertrand, a real estate developer. The candidates have similar views on several topics, but Bertrand has argued that voters are tired of King's brash statements on topics ranging from immigration to abortion.

Still, King goes into Tuesday with several endorsements from key Republicans in the state, including U.S. Sens. Grassley and Joni Ernst.

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STATE RACES

Every two years the bulk of the seats in the Iowa Legislature are up for grabs, though many incumbents face little challenge from within their respective parties. Tuesday's primary will mostly help shape up the general election battles to come for some lawmakers in November. Republicans lead in the House and Democrats hold the Senate. Like clockwork, both sides vow every election to take control of the other chamber. Expect such an effort to heat up in the Senate, where Democrats have a slim majority.

Tuesday's primary will mostly help shape up the election battles to come, including in western Iowa. Three candidates in a Republican primary are vying to challenge Senate Majority Leader Mike Gronstal, a Council Bluffs Democrat.