On Monday, Dianne Feinstein, the 84-year-old Democrat who has served as one of California's senators since 1992, announced her bid for reelection. She kicked off the campaign with a Beverly Hills fundraiser, which was met with, according to a local news report, "a small but energetic crowd of protestors... demanding that Feinstein endorse the Sanders bill for single-payer healthcare."

That shows the unexpected challenge Feinstein is facing. She's an influential Democrat who has in past decades pushed progressive causes like gun control and is currently the highest-ranking Democrat on the Senate Judiciary Committee. But now she's under siege from the leftists who have gained newfound power in her party—and a primary challenge against her, which is all but inevitable, could be a key battle in the struggle for the soul of the Democrats.

Unsurprisingly, Feinstein has already received support from the state's most notable Democrats, including Senator Kamala Harris, congressmen Adam Schiff and Ted Lieu, and Los Angeles mayor Eric Garcetti, who was one of the hosts of her Beverly Hills fundraiser. But activists have taken issue with what they see as her centrism, especially when it comes to her opposition to Bernie Sanders's Medicare for all plan. "If single-payer healthcare is going to mean complete takeover by the government of all healthcare, I'm not there yet," she said at a town hall in April. And that isn't the only thing that has Berniecrats ready to raise hell against her.

In 2014, she joined Republicans in opposing President Barack Obama's plan to reform spy agencies. She's long been sympathetic to the national security establishment, has been a strong backer of the PATRIOT Act and NSA wiretapping programs, and was one of many Democrats to vote for the Iraq War—a decision she recently told Mother Jones that she regrets.

That doesn't mean she isn't a liberal. She has a history of for stronger gun control laws after she witnessed the assassination of San Francisco mayor George Moscone and city supervisor Harvey Milk in 1978. She recently introduced a bill to ban bump stocks after they were found in the hotel room of Stephen Paddock, the shooter who killed 58 victims in Las Vegas. And she broke with the intelligence community in 2014 when she released a committee report on the CIA's post-9/11 torture program.

That's not enough for the latest generation of California Democrats, who are more left wing than their predecessors. Kimberly Ellis, an activist who unsuccessfully ran for California Democratic Party chair earlier this year, told the New York Times that "California has changed over the two and a half decades [Feinstein] has been in office, and I don't think she's changed along with the state."

That is at least partially borne out by polls. A September UC Berkley survey found that 50 percent of eligible voters approve of Feinstein's performance, but that same the Public Policy Institute of California found that only 41 percent of California voters—and 57 percent of Democrats—thought she should run for another term. Those aren't particularly bad numbers, but they might be just weak enough to convince an ambitious politician that she's vulnerable.

Ro Khanna, a freshman congressman who represents Silicon Valley and served in the Department of Commerce under Obama, is actively trying to recruit primary challengers to unseat Feinstein—an aggressive move that shows how eager the left is to defeat her. He told Vox's Jeff Stein, "Feinstein is out of touch with the grassroots of our party on economic policy and foreign policy. After 47 years in elected office and 25 years in the Senate, she continues to cling to office as a voice for the status quo."

In an interview with Politico, Khanna, who was an outspoken supporter of Sanders in the 2016 primaries, further criticized her for being "totally out of touch when the whole debate happened on encryption," referencing the conflict between Apple and the FBI after the San Bernadino shooting. That's just one example of the larger anti-Feinstein narrative that has emerged. Her opponents are attempting to paint her as out of touch, both with the changing times and her base, mostly without being explicit about her age.

In recent years, she's been attacked for holding positions that might once have seemed uncontroversial. In 2015, National Nurses United, the country's largest professional nurses union and a major player in progressive politics, put Feinstein on its "dishonor roll," along with several other Democrats after she voted in favor of authorizing the president to "fast track" global trade deals like the Trans-Pacific Partnership. California Senate leader Kevin de León criticized her after she told a San Francisco audience that she believes Trump "can be a good president."

On Thursday afternoon, CNN reported that León will challenge Feinstein in the primary. The report also suggested that billionaire environmentalist Tom Steyer is "very much looking at the Senate race."

But Feinstein doesn't seem too concerned with the leftist criticism she's received. "I have the energy," she told the New York Times. "My mind is fine. I believe I will have strong support from Democrats—and from others." That seems likely to be tested soon.

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