Alaska’s nonpartisan Senate primary will offer a rare chance to test the strength of the two leading candidates, Dan S. Sullivan, the Republican incumbent, and former Representative Mary Peltola, a well-funded Democrat, as they face off months before November.
And voters in Northern California will choose a replacement for former Representative Eric Swalwell, who resigned in the spring after allegations of sexual misconduct.
Here’s what to watch on Tuesday, a busy Primary Day from coast to coast.
Who’s ahead in Alaska’s marquee Senate race?
Alaska has nonpartisan Senate primaries, and the top four candidates will move on to the general election.
That means Mr. Sullivan, 61, and Ms. Peltola, 52, will face each other, along with a crowd of long-shot contenders, on the ballot on Tuesday.
The race is among a few expensive, high-profile contests considered the most likely to determine which party wins control of the Senate in the midterms.
Mr. Sullivan and Ms. Peltola are both widely expected to advance on Tuesday, but their vote shares will be closely watched as a reflection of who’s ahead going into the general election.
Also in question: Whether Dan J. Sullivan, a former educator with scant political experience, will win a spot on the general election ballot.
Republicans worry that voters will mistakenly cast ballots for Dan J. Sullivan thinking that they’re voting for Senator Sullivan, potentially lifting Ms. Peltola to victory in November.
In Florida, will Debbie Wasserman Schultz hold on?
Representative Debbie Wasserman Schultz of Florida, an 11th-term congresswoman and former Democratic National Committee chair, is trying to escape a crowded primary.
Her seat was eliminated when Republican state lawmakers gerrymandered the state’s congressional map in the spring, part of a coast-to-coast partisan redistricting battle.
Ms. Wasserman Schultz, 59, who is white, is now running in a historically Black district — against four Black Democrats.
One of them, Elijah Manley, 27, an educator who describes himself as a democratic socialist, has won the support of Representative Ro Khanna, Democrat of California, and is hoping for an upset.
What about Jared Moskowitz?
Representative Jared Moskowitz, a second-term Democrat, is also trying to capture a new district after his old one was eliminated in the redistricting wars.
Like Ms. Wasserman Schultz, the moderate Mr. Moskowitz, 45, is trying to fend off a younger challenger from the left. He is competing against Oliver Larkin, 34, a democratic socialist and union organizer.
The contests featuring Ms. Wasserman Schultz and Mr. Moskowitz could help determine whether any left-wing primary wave is crashing into Florida.
Will an embattled House Republican be unseated?
Representative Cory Mills, who is running for re-election in a district northeast of Orlando, is under investigation by the House Ethics Committee.
Last year he was investigated by the Washington, D.C., police after a woman filed a report of assault, though no charges were filed. And his former girlfriend was also granted a protective order against him.
This month, two Republican House members from Florida, Anna Paulina Luna and Mike Haridopolos, endorsed one of his rivals, Ryan Elijah, 54, a former local Fox TV news anchor.
But Mr. Mills, 46, who has denied any wrongdoing, maintains the endorsement of President Trump, a powerful force in Republican primaries.
Will Alexander Vindman become the Democratic nominee for Senate?
Florida, once a quintessential swing state, has shifted right over the past decade, and political analysts give Democrats remote odds of winning the Senate race there in the fall.
But some Democrats hope that Alexander Vindman, 51, a top witness in Mr. Trump’s first impeachment trial, will give their party a shot. Mr. Vindman, a former Army lieutenant colonel, has proved a strong fund-raiser.
But first, to advance to the general election, he must fend off a democratic socialist, State Representative Angie Nixon, 42, of Jacksonville, who has swept up endorsements from progressive Congress members and the popular children’s entertainer Ms. Rachel.
The winner of the Democratic Senate primary is expected to face Senator Ashley Moody, a Republican who was appointed to the former seat of Secretary of State Marco Rubio.
Who will replace Swalwell in California?
Four months ago, Mr. Swalwell resigned from Congress, giving up his Bay Area seat after sexual assault allegations, which he denied.
Now voters in the quiet suburbs of San Francisco will go to the polls to pick Mr. Swalwell’s replacement. The race pits State Senator Aisha Wahab, 39, a progressive backed by the California Democratic Party, against Melissa Hernandez, 51, a moderate supported by AIPAC’s main super PAC.
Ms. Wahab led Ms. Hernandez by 26 percentage points in a crowded nonpartisan primary in June. But the race has since been flooded with cash.
