Reps. Katie Porter, Adam B. Schiff and Barbara Lee all claim the progressive mantle, an almost essential ingredient for any politician hoping to put together a winning Senate campaign in a state that champions gun control, abortion rights, marriage equality and combating climate change. They face the difficult task of defining themselves in a heavily Democratic electorate that may struggle to distinguish what separates them.

“California is not going to elect a Republican. And they’re not going to elect a centrist. The question is what kind of progressivism is important” to voters, said Dan Schnur, a politics professor at UC Berkeley, USC and Pepperdine University. “These three candidates represent very different strains of progressivism.”

Porter, of Irvine, is a whiteboard-toting economic populist; Lee, of Oakland, is a longtime social justice activist; and Schiff, of Burbank, is an anti-Trump litigator focused on saving democracy, Schnur said. These personas are grounded in the lives they led long before they were elected to office.

Lee hasn’t entered the race, but has told colleagues that she plans to soon. Her activism dates back to her work on the 1972 presidential campaign of Shirley Chisholm, the first Black woman to hold a seat in Congress; and on the Oakland mayoral campaign of Black Panther Party co-founder Bobby Seale the following year. Lee, 76, was elected to the state Legislature in 1990 and to Congress in 1998.

She is best known for being the only member of Congress to vote against the measure that authorized President George W. Bush to use military force after the Sept. 11 terrorist attacks. Lee was viewed as a pariah by many afterward, and subjected to death threats, but her qualms about granting a president too much power are now echoed by politicians in both parties.

Schiff, 62, is a former federal prosecutor who was first elected to public office during President Clinton’s tenure, and who reflected the former Arkansas governor’s center-left views while serving in the California Legislature and when he was elected to Congress in 2000. Schiff gained national prominence as he led the first impeachment effort against then-President Trump in 2019 and served as a key inquisitor on the congressional panel that investigated the Jan. 6, 2021, insurrection at the U.S. Capitol.

Porter’s political views were indelibly shaped as she grew up on an Iowa farm during the farm crisis, and led to a prominent career as a law professor specializing in consumer protection. The 49-year-old single mom has hammered bank and pharmaceutical executives during congressional hearings, frequently using a whiteboard to break down complex issues.

A protege of Sen. Elizabeth Warren, Porter was appointed by then-California Atty. Gen. Kamala Harris as the state’s independent monitor of California’s share of a $25-billion mortgage settlement with banks.

Porter and Schiff are well-known to MSNBC viewers, Democratic activists and social media denizens — a picture of Porter nonchalantly reading a book titled “The Subtle Art of Not Giving a F—” during the House speaker election in January went viral. Lee’s foreign policy votes after 9/11 are celebrated by liberal voters as proof of courage to defend unpopular views in times of national crisis.

“It’s going to be interesting,” said Roger Salazar, a Democratic consultant who was a spokesman for former Gov. Gray Davis as well as for the Clinton-Gore White House. “You don’t have your business Democrat or your Reagan Democrat, so they’re going to have to really work hard to differentiate themselves from each other.”

The three lawmakers’ voting records are nearly identical, as are their views on reproductive rights, same-sex marriage and labor rights, so Californians should expect to see a major emphasis on pivotal issues and votes where they did diverge, as well as on campaign finance.

One contrast will be Lee’s post-9/11 votes with Schiff’s support of military action in Iraq and Afghanistan, as well as the Patriot Act’s ability to surveil American citizens. Another point of contention will be who backs their campaigns financially.

Porter refuses donations from corporate political action committees and federal lobbyists, while Schiff has received significant sums from committees representing businesses, including oil firms, payday lenders and pharmaceutical interests, according to campaign finance reports. A Schiff spokesman said he would not accept donations from corporate PACs for his Senate campaign.

The candidates will need to introduce themselves to the state’s 21.9 million registered voters, 47% of whom are registered Democrats, 24% Republicans and 23% who do not state a party preference, according to the California secretary of state’s office.

No prominent Republican has entered the race thus far, so candidates will need to appeal to liberals, moderates and independents alike, particularly in light of the state’s nonpartisan primary. The two contenders who receive the most votes in March 2024 will advance to the general election, regardless of party.

But it’s early — the filing deadline is Dec. 8, though candidates who are not wealthy self-funders would have to launch campaigns well before then to raise the tens of millions of dollars it takes to compete in such a vast state.

If a well-known Republican enters the race and consolidates the GOP vote in the March 2024 primary, it’s likely that only one Democrat will advance to the November general election.

Historically, it’s been difficult for a member of Congress to win a statewide election, since they each represent under 2% of California residents and are often little-known to voters in the rest of the state. Former President Nixon, elected to the Senate in 1950 before winning the White House in 1968, and former Sen. Barbara Boxer, who was elected in 1992 alongside Feinstein, are the most notable exceptions.

Democratic consultant Garry South noted that California is so big that state senators have nearly a quarter-million more constituents than members of Congress. Members of the Los Angeles County Board of Supervisors each represent well over a million more residents than a congressperson.

Most voters who are not watching cable TV or scrolling through social media don’t know Porter, Schiff or Lee, South said.

“If you walk two or three blocks outside the perimeter of any of their districts, no one is going to know who any of these members are,” he said.

To overcome that disadvantage, the candidates will need widespread and effective political advertising campaigns, and in a state with so many voters and expensive media markets, that will be extraordinarily expensive.

Schiff and Porter are among the most prodigious fundraisers in the House, though Porter had to spend a significant sum in a tight reelection race last year. Lee has not needed to raise large sums, given that her congressional district is among the most liberal in the nation and she has sailed to reelection for decades.

Committees unaffiliated with the campaigns that can raise unlimited sums are already being organized for Schiff and Lee, and likely for Porter as well.

In addition to money, political experts argue that gender and race could be major factors in the Senate race.

South questions just how they might factor in; the Democratic electorate is more female than male, and the state has been represented in the Senate for the vast majority of the last three decades by two women. He also questions whether voters will want to replace Feinstein, an octogenarian, with Lee, a septuagenarian.

“We have a U.S. senator who was the oldest person serving in the Senate,” he said. “I’m not sure voters want to trade her out for someone not quite as old, but up there.”

The mix of candidates in the 2024 Senate race — and whether additional well-known Democrats or prominent Republicans join the field — will be a major factor in the path each hopeful takes in the months ahead.

“They’re going to have to figure out what the ultimate field looks like before they decide what will have the most impact with voters,” Salazar said.

“Right now, it’s still in the newborn stage,” he added. “We don’t know what the baby’s going to look like yet.”