If you’re a progressive, getting an email fundraising pitch from MoveOn.org is like seeing the fog roll in through the Golden Gate. It seemingly happens every day at the same time.

But check out the name fronting one that just landed: Sen. Kamala Harris. Rookie senators aren’t usually asked to lend their name to pitches to MoveOn’s audience of 5 million, but the California Democrat is already paying dividends as the pitch is getting “an unusually strong” fundraising return, MoveOn Washington Director Ben Wikler told me Wednesday.

It’s another sign that in less than seven months on the job, the former San Francisco district attorney and California attorney general has become a star fundraiser for the Democrats, who are badly in need of a star. And a lot of that has to do with Harris shedding the word that has dogged her through her career: “cautious.”

Cautious because she felt her jobs as San Francisco and later California’s top law enforcement officer hindered her ability to express her political views as forcefully as she would have liked and as other progressives wished she would have.

“I almost feel like my hands are tied behind my back,” Harris told me in October.

She was freed from that restriction on election night when, in the face of Donald Trump’s unexpected win, Harris chose to forgo a victory lap. Instead, she cut through the gloom at her victory party by challenging her supporters: What should we do “when our ideals and our fundamental values are being attacked. Do we retreat, or do we fight? I say we fight. I intend to fight,” she said that night.

That message hit the right chord at the right time — the beginning of the resistance to Trump.

Her digital team sent out a post-election email sounding the same note and got “a crazy response,” strategist Sean Clegg said. So Harris’ team invested in growing the mailing list, which has seen an increase of more than 1,000 percent.

The momentum continued once Harris got to Washington. She was one of few politicians invited to speak at the huge Women’s March the day after Trump’s inauguration. She was forceful in opposing 18 of Trump’s 22 high-level nominations — only three senators opposed more.

And she’s burnished her growing national reputation by flashing her prosecutorial skills during a series of high-profile Senate hearings.

She grilled Sen. Jeff Sessions about his legal basis for refusing to answer questions. A TV audience of 20 million saw how she used her questioning of former FBI Director James Comey to build a case that Sessions acted inappropriately during investigations into Russian interference in the U.S. election.

But what perhaps boosted her profile most happened during her pointed questioning with the Senate Intelligence Committee of Deputy Attorney General Rod Rosenstein. Both Sen. John McCain, R-Ariz., and Chairman Sen. Richard Burr, R-N.C., interrupted Harris and chided her for not allowing Rosenstein to answer a question fully. Burr did the same thing when Harris questioned Sessions.

Apparently that kind of insolence isn’t tolerated from women in the old white guys club known as the U.S. Senate. Harris tweeted her exchange with Rosenstein, including being shushed by McCain and Burr, and it was retweeted more than 25,000 times.

“She speaks like an actual human being, and that’s an ever-valuable commodity in Washington, D.C. — and she doesn’t pull punches,” MoveOn’s Wikler said. “And that fits the national mood.”

Moments like that have helped her social media presence boom. Last July she had 134,865 Facebook followers. She has five times that many today. A year ago, she had 53,873 Twitter followers; today she has 10 times as many.

That type of digital reach has helped her blossom as a reliable fundraiser. Without having to hit the road to give stump speeches at fundraisers, Harris has raised $1.6 million online since election day, with an average contribution of $19. She’s dished out $600,000 to 23 of her Senate Democratic colleagues facing re-election, roughly half of whom sit in states that Trump won.

It is a gesture that will engender a lot of goodwill with her more senior Democratic colleagues because, as we know, nothing in Washington speaks louder than cash given to a re-election campaign. Especially from a freshman who just pulled into town.

This high-flying start has the East Coast media teeing up an endless series of “Is Harris going to run for president in 2020?” stories. Easy, now. The real story is that California’s junior senator is quietly building a base of support that will help her do her day job — and perhaps win or save a seat or two for Democrats in the Senate. Not bad for someone who hasn’t been there long enough to suffer through Washington’s July humidity.

Bill Burton, who served in the Obama White House and now works in Los Angeles, said that when he saw first-term Sen. Barack Obama, he realized he could be “one of the few people we could send anywhere in the country” to raise money.

Harris has that same potential, Burton said. “She has a broad appeal.”

But let’s not take the Obama-Harris comparison further than that. For now.

Joe Garofoli is The San Francisco Chronicle’s senior political writer. Email: jgarofoli@sfchronicle.com Twitter: @joegarofoli