California's primary battle for the Senate seat to replace Sen. Dianne Feinstein, who died last fall, is one to watch on Super Tuesday.

       Twenty-seven candidates have filed for the Feinstein seat. The four leading contenders are Democratic Reps. Adam Schiff, Katie Porter and Barbara Lee, plus Republican Steve Garvey, a former Major League Baseball player. They are running not only to fill Feinstein's 2025 open seat, but also to complete her term in the final weeks of 2024.

       This deep blue state has a top-two primary, meaning all candidates run against each other on the same ballot regardless of party. So the question is whether this will be a heated campaign between two Democrats or if Republican challenger Garvey will wiggle his way into the final two.

       MORE: What is Super Tuesday and why does it matter?

       Rep. Adam Schiff speaks to supporters at the headquarters of the advocacy group, the Coalit...Show more ---Show more

       Michael R. Blood/AP

       ？？A Republican hasn't won a Senate race in California since 1988. Of California's 22 million registered voters, 47 percent are Democrats compared to the 24 percent registered as Republicans, according to California's Secretary of State.

       This election has already become the most expensive in the state's history. Both Schiff, a leading voice in the two impeachments of former President Donald Trump, and Porter, who rose to prominence from her questioning of corporate leaders, have raised an impressive amount of money.

       Former baseball player Steve Garvey speaks during a televised debate for candidates in the s...Show more ---Show more

       Damian Dovarganes/AP

       According to FEC reports, Schiff has raised $29.8 million in net contributions as of mid-February, plus the $21 million he had left in his House account. Porter, meanwhile, has collected $16.7 million -- combining that with $7.4 million she had left over after her reelection win in 2022. Lee, who is one of the most progressive voting records in the House, has raised only $4.8 million in net contributions.

       Schiff has used his haul to launch a heavy ad campaign that labels Garvey as a threat to Democrats in Congress.

       Porter, who is 2 points behind Garvey according to 538's polling average, and Lee, who is trailing the pack by a large margin, are the two main progressives in the fight. Both Porter and Lee have said Schiff's anti-Garvey ads could embolden Republicans and encourage higher voter turnout among that base, thus jeopardizing tight down-ballot races. A Garvey win could also deliver Schiff an easier general election win, they have added.

       MORE: 12 Super Tuesday primaries to watch in California and Alabama

       U.S. Senate candidate, Rep. Katie Porter (D-CA) speaks to members of the media during a ca...Show more ---Show more

       Josh Edelson/Getty Images

       Porter has repeatedly labeled the tactic as "brazenly cynical" and has coined it the "Schiff gift."

       "This weakens confidence in democracy," Porter said in an interview with MSNBC on Monday. "We are already seeing that in this election, that having Steve Garvey on the ballot will turn out Republicans. So that's a big deal for us down ballot and in winning back the House of Representatives."

       She argued that "having a strong Democratic race with two Democrats running all the way through November will give us a chance to talk about the issues that matter to California and how we can change how our politics works."

       Schiff and his allies have spent more than $11 million on ads -- with 60% of them targeting Garvey, according reporting from The Washington Post.

       Rep. Barbara Lee speaks during a televised debate for candidates in the senate race, Jan. 22...Show more ---Show more

       Damian Dovarganes/AP

       Through all of it, Garvey has surged 5 points in the polls since early February, according to 538's polling average.

       A winner in the contest will likely not be announced on Super Tuesday. Californians overwhelmingly vote by mail. Those ballots can be postmarked up to and including Election Day. They're counted as long as the ballot arrives within seven days (for the primary, that's Tuesday, March 12). This means the race could take several weeks to fully count.