Sen. Barbara Boxer Barbara Levy BoxerThe Hill's Morning Report - Presented by Facebook - Biden, Harris launch Trump offensive in first joint appearance Bottom line Polls show big bounce to Biden ahead of Super Tuesday MORE’s (D-Calif.) retirement is setting off a chaotic scramble to replace her — and could lead to a crowded, outrageously expensive race.

Boxer is one of a number of California Democrats who have reigned over the state for decades, leading to a lot of pent-up political ambition for younger members of her party. With her gone, that energy is about to explode.

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“It will be a very expensive race and it will be a crowded field,” former Rep. George Miller (D-Calif.), a close friend of Boxer’s, told The Hill. “There will be a lot of really talented people who will be vying for this seat.”

Democrats are buzzing about both California Attorney General Kamala Harris (D) and California Lt. Gov. Gavin Newsom (D), two rising stars, as early front-runners should they jump in. Billionaire environmentalist Tom Steyer is also signaling interest in a campaign.

Whoever takes the plunge will need lots of cash. California has long been one of the most expensive states in the nation to campaign due to its huge population and multiple media markets, and political campaigns’ prices have risen exponentially in recent years with the advent of super-PACs.

On top of that, California’s new “jungle” primary system — where the top two candidates advance regardless of party — has proven to be a money suck in other races, as everyone has to spend heavily to try to make it through both rounds.

Strategists are predicting the race will be the most expensive in history, with some mentioning $1 billion in total spending as within the realm of possibility, depending on who runs.

“That's one thing the new primary system has brought us — an incredible extra expenditure of money, which is unfortunate,” said Miller.

That could also yield some surprises. A pair of Democrats could advance to the fall election if no Republicans mount a serious bid, scrambling campaign strategy; a primary race to the left could quickly flip to a focus on independents for both candidates.

In addition to Harris, Newsom and Steyer former Los Angeles Mayor Antonio Villaraigosa (D) may be in the mix, along with California Secretary of State Alex Padilla (D). And Golden State Democrats say L.A. County supervisor Hilda Solis (D) and Reps. John Garamendi John Raymond GaramendiWuhan is the final straw: The world needs to divest from China GOP seizes on 'defund the police' to galvanize base Peace Corps faces uncertain future with no volunteers in field MORE, Loretta Sanchez, Raul Ruiz, Adam Schiff Adam Bennett SchiffTop Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Overnight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings Overnight Defense: House to vote on military justice bill spurred by Vanessa Guillén death | Biden courts veterans after Trump's military controversies MORE and Jackie Speier have all hinted they may look at a statewide bid.

Harris and Newsom each have higher aspirations, say Democrats, but are unlikely to both run. They share a common fundraising and political base in northern California, as well as a top consultant — longtime Democratic guru Ace Smith — and have made public signals that they won’t take each other on.

“I do not think Newsom would run against Harris and vice versa. I think they'll sit down and discuss how not to. They have great admiration for each other politically and they'll work it out,” said Joe Cotchett, a top northern California Democratic donor who described both as friends.

Harris recently swore in Newsom to a new term, a public sign that there is “peace in the valley,” as one senior California Democrat put it. A number of Democrats predicted that Harris will likely have the right of first refusal and will choose between the Senate race and waiting for a gubernatorial run in 2018.

If she decides to run for the Senate she’ll likely scare off more opponents because of her profile as a female, African-American hero of the liberal base.

Observers say Newsom may face a more crowded field.

“I think there's a likelihood the lieutenant governor will run, Gavin Newsom. I think there's a high likelihood that Antonio Villaraigosa ... may run. I hear there are a couple of House members who may run,” Sen. Dianne Feinstein Dianne Emiel FeinsteinMcConnell says Trump nominee to replace Ginsburg will get Senate vote Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Intensifying natural disasters do little to move needle on climate efforts MORE (D-Calif.) told reporters on Thursday. “And it's a different thing because have this open primary system. ... My last race was the first one along those lines. It's a bit hard to predict how people do in that kind of a race.”

Steyer is a big question mark. The billionaire, who spent more than $70 million in last year’s midterm elections supporting “green” candidates, could self-fund in a huge way and alter the trajectory of the race. He put out a statement praising Boxer soon after her retirement announcement, a sign he’s keeping a close eye on the race’s developments, and a Steyer ally predicted he will "take a look at it and consider it over the next few days or so." But Democrats speculated he wouldn’t run — and pointed out that most self-funding candidates have flamed out in California in recent years.

Whether Harris or Newsom takes the plunge, strategists expect a Los Angeles-area Democrat to jump in and carry the torch for southern California. Villaraigosa, a former L.A. mayor and Democratic National Committee vice chairman, is the biggest name in that group, and recently moved back to California to reengage in politics there. Sources close to the former mayor say he hasn’t ruled out a Senate bid, but that he’s much more interested in being governor. Who else jumps in may play a deciding role in what Villaraigosa does.

“He indicated to me the other day he was more interested in governor. But you know how he is, he changes daily,” said one source close to Villaraigosa.

The other Democratic candidates eyeing a bid don’t have the same type of statewide name recognition and may wait to see what the heavier hitters decide to do before making their own decisions. Garamendi said in a statement he will weigh a bid, while Speier refused to say if she’s considering a campaign in a brief interview with The Hill.

While the Democratic field is just starting to develop, the GOP’s short bench is already winnowing, and Republicans privately admit it’s unlikely they’ll be able to compete for the seat even with a top recruit.

“I don't know of anyone serious who'd want to take on that thankless job. The real story is going to be the Democratic primary,” said one California GOP strategist.

Former Secretary of State Condoleezza Rice’s spokeswoman told The Hill she’s definitely not interested in a race, while sources close to Rep. Darrell Issa (R-Calif.) also said there’s no way he’ll run.

The cost of the race also means that a self-funding candidate would be preferable for the party, though it’s unclear who that might be. Republicans also mention San Diego Mayor Kevin Faulconer, self-funding 2014 gubernatorial nominee Neel Kashkari and 2010 self-funding candidate Steve Poizner as potential candidates, though neither has signaled any interest in a bid.

One potential name not mentioned by strategists: former Rep. Mary Bono (R-Calif.), who lost her reelection bid in 2012. Bono sent a cryptic tweet on the race Thursday evening saying her party needs “a strong candidate” for the race, though a friend of hers said that she was worn thin on congressional politics and said it would "take an awful lot" to convince her to run.

—Mike Lillis and Julian Hattem contributed.