At the top of the ballot in California is the race to replace Gov. Jerry Brown, a term-limited Democrat. The big question on Tuesday is not so much who will place first — that’s almost certain to be Lt. Gov. Gavin Newsom, a former mayor of San Francisco — but who will place second. Under California law, the top two primary finishers advance to the general election, regardless of party.
If a Republican — probably John Cox, a business executive endorsed by President Trump — places second, Mr. Newsom should coast to victory in November in a state as blue as California. But if his main Democratic challenger, former Mayor Antonio Villaraigosa of Los Angeles, takes that spot, the general election could be much closer.
There is no such drama in Senator Dianne Feinstein’s re-election bid. Ms. Feinstein is broadly expected to win a sixth term over former State Senator Kevin de León, a fellow Democrat. No Republican candidate is expected to make it out of the primary.
Finally, Democrats are targeting seven Republican-held House districts that Hillary Clinton won: Districts 10 and 21 in the Central Valley; District 25 in Los Angeles County; Districts 39, 45 and 48 in Orange County; and District 49 in Orange and San Diego counties. Keep a close eye on Districts 39 and 48, where the sheer number of Democratic candidates has party officials scared that two Republicans will advance on the back of a splintered Democratic vote.
Representative Jeff Denham is seeking a fourth term in California’s 10th District, an area of the Central Valley centered on Modesto, and three Democrats are vying to challenge him: Michael Eggman, a farmer who has run against Mr. Denham twice before; Josh Harder, a venture capitalist; and Virginia Madueño, a public relations executive. The race was close in 2016, and Hillary Clinton won the district, making it a target for Democrats this year.
On paper, the Republican incumbent in the 21st District, David Valadao, should have no trouble winning re-election — especially because his only Democratic opponent, T.J. Cox, lives two districts north of this one, in the Central Valley. But Mrs. Clinton won the district handily, and the question in November will be whether President Trump is a heavy enough burden to drag Mr. Valadao down against the odds.
Three Democrats — Bryan Caforio, a lawyer who also ran in 2016; Katie Hill, who runs a homeless services nonprofit; and Jess Phoenix, a volcanologist — are running to unseat Representative Steve Knight, a member of the House Science Committee. This district, just north of Los Angeles, is one of national Democrats’ biggest targets, and they are worried that voters won’t choose the candidate with the best chance of winning in November.
It’s a free-for-all in Orange County’s District 39, where Representative Ed Royce, the incumbent Republican, is not seeking re-election. On the Republican side are State Senator Bob Huff; Shawn Nelson, a county supervisor; and former Assemblywoman Young Kim. On the Democratic side, the main candidates are Gil Cisneros, a philanthropist, and Mai Khanh Tran, a pediatrician — but quite a few other Democrats are running, too, creating the risk of a splintered vote that would allow two Republicans to advance to the general election.
The race in District 45, also in Orange County, has focused largely on health care since the incumbent Republican, Representative Mimi Walters, voted to repeal the Affordable Care Act. Her potential Democratic opponents include Brian Forde, a science adviser to President Obama; Dave Min, a law professor; and Katie Porter, also a law professor. Ms. Walters won easily in 2016, but Mrs. Clinton also won the district.
Democrats see this Orange County seat — held by Representative Dana Rohrabacher, who is close to Mr. Trump and has been tied to Russia and WikiLeaks — as one of their best pickup opportunities in November. The problem is getting one of their candidates, like the biomedical researcher Hans Keirstead or the businessman Harley Rouda, to November. There is a second Republican in the race, Scott Baugh, and California’s jungle primary could let him lock Democrats out of the general election altogether if he and Mr. Rohrabacher place first and second on Tuesday.
The field is crowded for the Southern California seat being vacated by Representative Darrell Issa. State Assemblyman Rocky Chávez and a Board of Equalization member, Diane Harkey, are vying to keep the district in Republican hands. Running against them are a passel of Democrats, including the Marine veteran and 2016 candidate Doug Applegate; Sara Jacobs, a former adviser to Mrs. Clinton; Paul Kerr, a businessman; and Mike Levin, a lawyer. As in District 48, Democrats are worried that their crowded primary will let two Republicans advance.