Backers of Sen. Dianne Feinstein have moved to form a super PAC for her re-election next year — not so much to beat back the just-announced challenge by fellow Democrat Kevin de León, the state Senate president, as to arm for possible war against billionaire environmentalist Tom Steyer.

“Steyer is the real issue that is stalking her right now,” said Sean Clegg, a partner in the political consulting firm SCN Strategies. “This is a guy who spent north of $70 million on Senate and gubernatorial races all around the country in 2014 election cycle, so he has a proven track record of unlimited spending.”

Steyer, who lives in San Francisco and made his money as a hedge fund manager, hasn’t said whether he’ll make a run at Feinstein. But he’s definitely thinking about it.

“I am looking at the best way to take our government back from the political establishment and to stop Donald Trump. That includes a full consideration of running for the United States Senate,” Steyer said in a statement over the weekend.

Clegg’s SCN is helping to set up the pro-Feinstein super PAC, which can spend unlimited amounts on her behalf as long as it doesn’t coordinate its activities with her. SCN isn’t running the senator’s campaign — that’s the job of her longtime strategist, Bill Carrick.

There’s no doubt that Steyer could spend major money in a run against Feinstein. All he has to do is tap his own bank account — there are no limits to how much candidates can spend on their own campaign.

Steyer’s billions give him a major advantage over de León, who has no personal fortune to draw upon and must raise cash in small chunks. Even Feinstein, whose worth is in the neighborhood of $79 million, could have a hard time matching Steyer’s spending dollar for dollar, though her campaign says she is willing to self-fund.

But if money alone could buy an election, we’d be wrapping up Gov. Meg Whitman’s second term. Longtime pollster Mark DiCamillo notes that there are some things money can’t buy — such as name recognition.

“They may have the resources, but they don’t have a very large name identification with voters,” DiCamillo said of the long list of wealthy, self-funded candidates who have failed in runs for office in California in the past 25 years. “That is something that takes time.”

A Steyer challenge would not be the first time Feinstein has faced off with a multimillionaire. In 1994, Republican Michael Huffington (the then-husband of Arianna Huffington) spent $28 million of his own money running against Feinstein. She won re-election, by a mere two percentage points.

This time, Feinstein’s supporters want to be ready. But the super PAC solution has the potential for backfiring.

A super PAC can be a conduit for funneling special-interest money into a race, and special interests can be an embarrassment. Picture the headlines, for example, if ExxonMobil decided to funnel big bucks to Feinstein through an “unaffiliated” super PAC.

But they are popular with the political set. De León backers Maclen Zilber and Dave Jacobson at the J&Z Strategies consulting outfit in Los Angeles have set up a super PAC for the state Senate president.

“We will be looking to raise on a small and on a larger scale from everyone from progressives to environmental organizations to organized labor,” Zilber said. “Everyone fed up with the status quo.

“The goal is to bring in as much good money as we can.”

With Feinstein racking up early endorsements from such big names as Democratic U.S. Sen. Kamala Harris and Los Angeles Mayor Eric Garcetti, de León can take heart that he’s won the backing of a prominent Bay Area Democrat, Rep. Ro Khanna of Fremont.

Khanna knows what it’s like to take on an establishment Democrat — he did it twice, losing to Rep. Mike Honda in 2014 before beating him in a rematch two years later.

“She should have a challenge,” Khanna said of Feinstein. “We need new voices. We need a vigorous debate.”

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call (415) 777-8815, or email matierandross@sfchronicle.com. Twitter: @matierandross