One factor – perhaps the decisive one – in Dianne Feinstein’s decision to seek another term in the U.S. Senate next year was pressure from party leaders, who feared an expensive and divisive free-for-all were she to retire.

Democrats have three dozen Senate seats up next year, will be financially stretched to defend the most vulnerable and have been counting on big bucks from California’s wealthy liberals, particularly those in entertainment and high-tech, to meet fundraising goals.

Never mind.

Kevin de León’s bold – or cheeky – challenge to Feinstein guarantees that heavy money will be raised and spent in California next year. And it could get even more expensive if billionaire Tom Steyer also jumps into the Senate race.

It’s conceivable that with de León, the president pro tem of the state Senate, and possibly Steyer challenging her, the 84-year-old Feinstein might decide that she doesn’t want the hassle of another Senate race after all. She has acknowledged that she had seriously thought of retiring.

Conversely, Feinstein, who’s been under fire from the rambunctious uber-liberal wing of her party, could feel insulted and run again just to prove that she won’t be bullied.

Assuming she stays the course – her campaign manager described de León as “a termed-out politician looking for a gig” – the stage is set for a two-, three- or even four-way donnybrook that will consume tens of millions of dollars that party leaders had hoped would be available for use elsewhere, including unseating some Republican congressional members in California.

It would also exacerbate what was already a serious bitter rupture between the state’s Democratic establishment, which Feinstein personifies, and the self-proclaimed “progressives” who identify with failed presidential candidate Bernie Sanders.

While Feinstein is, at this early point, the favorite, these are tumultuous times in California politics as Democratic politicians vie to be President Donald Trump’s most vociferous opponent. De León devoted Sunday’s announcement to denouncing Trump and didn’t even mention Feinstein.

There are multiple scenarios possible, depending on whether Steyer and/or another wealthy figure, such as wealthy investor Joe Sanberg, jump into the race, whether Republicans mount even a token effort and the effect of California’s top-two primary system.

If it’s just Feinstein and de León on the Democratic side, and with several lightweight Republicans, it will almost certainly be a Democrat vs. Democrat finale in November 2018.

That would be superficially similar to what happened last year, when Kamala Harris won a Senate seat, but unlike 2016, a 2018 duel would probably involve two well-financed combatants.

If it’s a three- or four-way Democratic duel, and there’s just one more or less reasonable Republican on the ballot, chances are that the top Democratic vote-getter will face only the GOP candidate in November and win easily.

At the moment, de León has to hope that he will be Feinstein’s only serious Democratic challenger, because she won’t have any trouble raising money for a re-election campaign while he starts at zero, unable to shift state campaign money he’s already amassed into a Senate race.

De León needs to capitalize on being the toughest anti-Trump candidate, but if one or two wealthy, self-funded candidates also run, it will make his positioning and fundraising infinitely more difficult.

A final note: Now that he’s declared for the U.S. Senate, de León can’t hang onto his leadership position in the state Senate very long, and once he’s lost that, his fundraising leverage takes a hit.

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Dan Walters has been a journalist for more than 60 years, spending all but a few of those years working for California newspapers. He began his professional career in 1960, at age 16, at the Humboldt Times...