Eight states are hosting primaries Tuesday, but all eyes will be on California — where the threat of Democrats getting shut out of a few top pickup opportunities they hope will help them win back the House looms large.

Several matchups will also be decided in competitive general election contests in Iowa, New Jersey, New Mexico and Montana.

Primary races for safe Republican and Democratic seats could determine some likely new members of Congress. And Alabama Rep. Martha Roby is being challenged by four fellow Republicans, with the prospect of a prolonged primary campaign if she is forced into a runoff.

Here are four things to watch as the results from the eight states holding primaries come in:

1. California chaos

Democrats view the Golden State as key to winning back the House and are targeting 10 GOP-held districts, including seven that Hillary Clinton carried in 2016. Four districts touch Orange County, which was long considered a Republican stronghold.

But California’s top-two primary system has caused some headaches for Democrats. The two candidates who garner the most votes advance to the general election, regardless of party. So with multiple contenders on both sides, Democrats are worried their candidates will split the vote, allowing two Republicans to advance.

Democrats were scrambling to avoid a shutout in three Orange County districts: the 48th, held by GOP Rep. Dana Rohrabacher; the 39th, held by retiring GOP Rep. Ed Royce; and the 49th, held by retiring GOP Rep. Darrell Issa. Inside Elections with Nathan L. Gonzales rates both open seats as Toss-ups, while the race in the 48th is rated Tilts Republican.

Democrats will also be choosing nominees in four other GOP-held districts that backed Clinton. Of those, two are in the Central Valley — Rep. Jeff Denham’s 10th District and Rep. David Valadao’s 21st — and two in Southern California — Rep. Mimi Walters’ 45th District and Rep. Steve Knight’s 25th. Some operatives believe Knight could be the most vulnerable GOP incumbent in the state.

Watch: California’s 25th District Diverse in Candidates, Constituents and Land

Other races to watch include Democratic primaries to take on three GOP incumbents: Rep. Duncan Hunter, who is under federal investigation for misuse of campaign funds, in the 50th District; Rep. Tom McClintock in the 4th District; and Rep. Devin Nunes in the 22nd District. But those seats are considered more of a reach for Democrats given their Republican lean.

2. General election matchups

Iowa’s 1st District

Tuesday’s primaries could determine the Democratic nominees in two competitive Iowa races — or they might not. If a candidate does not garner 35 percent of the primary vote, the nominee is decided at a state party convention on June 16.

1st District Rep. Rod Blum is one of the most vulnerable Republican incumbents. State Rep. Abby Finkenauer was added to the Democratic Congressional Campaign Committee’s Red to Blue program for promising recruits back in November and she has been endorsed by EMILY’s List. She has raised the most of the four Democrats in the race.

Thomas Heckroth, who worked for the Obama Labor Department as well as for former Democratic Sen. Tom Harkin, is also running, as are Army veteran George Ramsey and Courtney Rowe, an engineer who served in the Air Force Reserves. Inside Elections rates the general election a Toss-up.

Iowa’s 3rd District

Elsewhere in the Hawkeye State, Democrats are competing to take on GOP Rep. David Young, also a target. A signature-gathering issue tossed one top contender off the Democratic primary ballot, leaving three to compete for the nomination.

Small-business owner Cindy Axne, who has been endorsed by EMILY’s List, had the most cash on hand heading into the primary, followed by Eddie Mauro, who heads an insurance company. Also in the mix is Pete D’Alessandro, who worked for Vermont independent Sen. Bernie Sanders’ 2016 presidential campaign. Inside Elections rates the race Likely Republican.

New Mexico’s 2nd District

Republican incumbent Steve Pearce’s decision to run for governor opened up his seat, which Democrats are targeting this year. President Donald Trump carried the district by 10 points in 2016. The DCCC added lawyer Xochitl Torres Small to its Red to Blue program in February. She faces Madeline Hildebrandt, a Coast Guard veteran and community college instructor, in the Democratic primary.

A number of well-funded candidates are facing off on the Republican side, including state Rep. Yvette Herrell, who has been endorsed by the House Freedom Caucus; Monty Newman, a onetime chairman of the New Mexico Republican Party; and Gavin Clarkson, a former Trump administration official. Inside Elections rates the race Leans Republican.

New Jersey’s 2nd District

Democrats feel confident about their prospects in this open seat now that 12-term GOP Rep. Frank A. LoBiondo is retiring. The general election race is rated Tilts Democratic. Another DCCC Red to Blue candidate, state Sen. Jeff Van Drew, who has a moderate record in the state Legislature, is expected to win the Democratic primary over three opponents including retired teacher Tanzie Youngblood, who has the support of the Congressional Black Caucus PAC. Van Drew has a large cash-on-hand advantage over Republican Hirsh Singh.

New Jersey’s 3rd District

Democrat Andy Kim, a former National Security Council official, faces little opposition to take on GOP Rep. Tom MacArthur in this Likely Republican race. The DCCC added him to Red to Blue in February.

New Jersey’s 5th District

Freshman Rep. Josh Gottheimer is one of the Republicans’ few targets this year. The National Republican Congressional Committee added perennial candidate Steve Lonegan to the second tier of its Young Guns program for strong recruits. The former mayor of Bogota previously ran for Senate, governor and another New Jersey congressional district. He led the GOP field in fundraising, and has endorsements from Sens. Ted Cruz and Rand Paul, and Corey Lewandowski. The general election is rated Leans Democratic.

New Jersey’s 7th District

After several other Democrats dropped out of the primary, Tom Malinowski looks likely to take on GOP Rep. Leonard Lance in this Tilts Republican race. The former assistant secretary of State for democracy, human rights and labor was added to Red to Blue in April.

New Jersey’s 11th District

Mikie Sherrill, a former prosecutor and Navy pilot, is the Democratic favorite in this longtime Republican seat that’s open because of Rep. Rodney Frelinghuysen’s retirement. She was an early addition to Red to Blue. Family advocate Tamara Harris has the backing of California Sen. Kamala Harris, the Congressional Black Caucus PAC and the backing of Collective PAC, which backs African-American candidates. The NRCC put three candidates on the first level of its Young Guns program, with state Assemblyman Jay Webber raising the most money. The general election is rated Tilts Democratic.

Montana’s at-large district

Democrats are jockeying to take on freshman Rep. Greg Gianforte, the Republican who won last year’s special election for the at-large House seat the day after physically assaulting a reporter. Lawyer John Heenan is from Billings and has endorsed “Medicare for all” legislation. Nonprofit executive Grant Kier is a former land trust director from Missoula. Former state Rep. Kathleen Williams is from Bozeman and has made her opposition to the National Rifle Association and support for an assault weapons ban part of her campaign. The general election is rated Likely Republican.

3. Senate primaries

Montana

Montana is one of the last states to host a competitive GOP Senate primary. The internecine battle here hasn’t been anywhere near as nasty as Republican contests in Indiana and West Virginia earlier this year, but late outside spending has intensified the race between front-runner Matt Rosendale, the state auditor, and former judge Russ Fagg. The Club for Growth’s political arm has spent more than $1.6 million backing Rosendale and attacking Fagg.

Meanwhile, Fagg’s campaign has pointed to the outside support for Rosendale to attack his ties to Montana. (He moved to the state in 2002.) There’s been scant polling released here, except for surveys conducted for Rosendale or groups supporting him. The winner will take on Democratic Sen. Jon Tester in a Tilts Democratic race.

California

Democratic Sen. Dianne Feinstein is expected to finish first in the crowded primary for her Senate seat in California, but it’s anyone’s guess who might come in second to challenge her in November. A whopping 32 candidates qualified for the ballot, and it’s unclear if a Republican will advance, thanks to the state’s top-two primary system.

Democratic state Sen. Kevin de León is challenging Feinstein from the left, so an intraparty fight could ensue if he makes it to the general election ballot. Inside Elections rates the race Solid Democratic.

4. Safe seats

Alabama’s 2nd District

GOP Rep. Martha Roby has drawn four primary challengers mainly over her criticism of Trump during the 2016 campaign. After a tape of Trump bragging about grabbing women by the genitals was made public, Roby said she would not vote for him and he should no longer be the GOP nominee.

The question for Roby is whether she will win more than 50 percent of the vote, or be forced into a primary runoff with one of her challengers. State Rep. Barry Moore, Roy Moore’s campaign manager Rich Hobson, Iraq War veteran Tommy Amason and party-switching former Rep. Bobby Bright, who represented the 2nd District for a term as a Democrat, are all taking on Roby. Trump carried the district by 32 points.

South Dakota’s at-large district

Republican incumbent Kristi Noem is vacating her at-large seat to run for governor. The winner of Tuesday’s GOP primary will be in a strong position for November. Former state Public Utilities Commissioner Dusty Johnson and Secretary of State Shantel Krebs have raised the most of the three-person primary field — both pulling in more than $600,000. Krebs has been touted as a top female recruit in a year when GOP women are looking to boost their ranks in the House following a number of retirements.

Mississippi’s 3rd District

GOP Rep. Gregg Harper’s decision not to seek re-election opened up his 3rd District seat. Six Republicans are running, which means the primary is likely to advance to a runoff between the top two finishers on June 26.

Whoever wins is likely coming to Congress in 2019. Harper has donated to District Attorney Michael Patrick Guest, who’s also secured financial support from a few other conservative House members from other states. Three of the Republicans running are women, but no outside groups have come in to help them get through the primary. State Sen. Sally Doty has support from Indiana Rep. Susan W. Brooks.

New Mexico’s 1st District

Democratic Rep. Michelle Lujan Grisham is running for governor, leaving behind a safe Democratic seat in Albuquerque. Six of the Democrats in the race have raised more than $200,000 and the primary has attracted nearly $2 million in outside spending. The bulk of outside money has been spent supporting or opposing Damon Martinez, an Army veteran and former U.S. attorney.

Veterans groups including the With Honor Fund, a bipartisan group, and VoteVets, which backs liberal veterans, have backed Martinez. EMILY’s List has spent against him, even though it has not endorsed a candidate in the race.

Former law professor Antoinette Sedillo Lopez has raised more than $1 million in her race. She has been endorsed by the political arm of the Congressional Hispanic Caucus and liberal groups including the Our Revolution and Working Families Party chapters in New Mexico. Former state Democratic Party Chairwoman Deb Haaland is also a top candidate and would be the first Native American woman elected to Congress if she wins.