California Politico rounds up the evidence:

In the years since California adopted a top-two primary system — which allows the highest vote-getters to advance to the general regardless of party — campaigns have perfected the art of strategically elevating the opponent they’d most like to face in November. That often takes the form of “attack” ads that actually serve to elevate a desired, further-right foe among his conservative base. Another cycle has brought a fresh round of machinations and accusations. Depending on whom you ask, it’s the type of disingenuous and cynical tactic that toxifies politics for most voters — or it’s just savvy strategy.

Republicans gathered yesterday to decryDemocratic Assembly member Kevin Cooley’s move on this front. The moderate Democrat looks vulnerable to a challenge from Capitol GOP chief of staff Joshua Hoover in a D+5 district during a Republican-tilting year. But a mailer from Team Cooley doesn’t mention Hoover. It spotlights Republican Jeffrey Perrine as “a pro-Trump patriot who calls himself an ‘anti-establishment’ conservative,” noting Perrine got booted from a local GOP organization without clarifying it was after Perrine was outed as a Proud Boy. Cooley “is playing with fire,” Hoover warned. He is “better than this,” Assembly Republican leader James Gallagher added.

Allies of Attorney General Rob Bonta are following a similar script.Few analysts think conservative Republican attorney Eric Early is best positioned to ride public safety concerns to unseating Bonta — no-party-preference Sacramento District Attorney Anne Marie Schubert is seen as the bigger threat, or Republican former U.S. Attorney Nathan Hochman. Hence a labor-funded, pro-Bonta PAC spending nearly $750,000 so far attacking Early, including with spots that call Early a “Trump Republican” who will “end Obamcare” and for whom “protecting the Second Amendment is everything.” Another pro-Bonta PAC has run radio spots nominally stumping for Bonta while characterizing Early as the “pro-Trump, pro-guns, pro-life” candidate.

So it goes. A primer on earlier iterations: Gov. Gavin Newsom “assailing” Republican John Cox in 2018 for standing “with Donald Trump and the NRA,” sidestepping well-funded Democratic challenger Antonio Villaraigosa and going on to crush Cox in November. National Democrats in 2018 “attacking” Assembly member Rocky Chavez for backing a gas tax increase, after which Republican BOE member Diane Harkey made the general and lost by 13 points. A 2020 mailer promoting an obscure Republican in the open, heavily Democratic CA-53. Real estate players spending around $175,000 in the last primary boosting the scandal-beset Democratic former Assembly member Steve Fox, who in November didn’t come close to knocking GOP Assembly member Tom Lackey from a D+11 seat.

California doesn’t hold a monopoly on this strategy. Pennsylvania Democrat Josh Shapiro just deployed it effectively in the state’s gubernatorial race, funding ads that helped get hoped-for Republican Doug Mastriano into the general by “blasting” him as “one of Donald Trump’s strongest supporters.” But the particular vagaries of the top-two system have helped make it a campaign season fixture as reliable as recycling bins overflowing with mailers.