The battle lines for the 2020 presidential campaign are forming. On one side are Democrats who want Medicare for All, tuition-free college and a Green New Deal that would cut way back on fossil fuels, and call for raising taxes on the wealthy to pay for it all.

On the other side: billionaire possible candidates who deride such ideas as “not a practical thing” (ex-New York Mayor Michael Bloomberg on Medicare for All,) “un-American” (former Starbucks CEO Howard Schultz on same) and, of course, President Trump. He road-tested a 1950s-style attack line for 2020 in his State of the Union address when he declared, “America will never be a socialist country.”

Historically, when Democrats are accused of being too far left, they roll up into a weepy ball. In the 1988 presidential race, President George H.W. Bush dogged Democratic nominee Michael Dukakis as a “card-carrying member of the ACLU.” Dukakis complained weakly, “I resent it.”

Resenting it isn’t the same as fighting back, which is what a new generation of progressives is doing. They are embodied by Rep. Pramila Jayapal.

In just her second term, the 53-year-old Seattle Democrat has become one of the nation’s leading left-wing voices as co-chair of the House Progressive Caucus. She’s writing one of the House’s soon-to-be-introduced Medicare-for-all bills and is on the forefront of progressive battles on immigration, impeachment, green energy jobs and ending U.S. military involvement in Yemen.

And she’s got the respect of House Speaker Nancy Pelosi of San Francisco, who calls Jayapal “a champion” for her advocacy.

Jayapal doesn’t hide from the left label. Instead, she turns opposition to progressive causes into deal-breakers.

She’s not afraid to take on allies like Ohio Sen. Sherrod Brown, a fellow progressive who, like most Democrats in the Western Hemisphere, is exploring a White House run.

Instead of supporting Medicare for All, Brown wants to lower the age for Medicare eligibility from 65 to 55. That sets him apart from other White House hopefuls like Sens. Kamala Harris of California, Elizabeth Warren of Massachusetts, Kirsten Gillibrand of New York and Bernie Sanders of Vermont, and former Obama administration official Julián Castro.

During a recent trip to Iowa, Brown said, “Democrats simply aren’t talking to working-class families. ... It’s almost like this view that you either talk to the progressive base to excite them or you talk to working-class families and you hear about their families and their problems. And, no, you’ve got to do both."

In an interview for The Chronicle’s “It’s All Political” podcast, Jayapal was dismissive.

“I don’t know what Sherrod Brown has eaten for breakfast that he is separating progressives and working people,” Jayapal said. “The last time I looked, progressives are working people. There are lots of people struggling to make it every day.”

She has little patience for those who say now isn’t the time for big ideas. Not when 40 percent of the population is underinsured for health care.

“People are dying because they can’t afford health care,” she said. “Of course, big ideas take time to push along. Some of the greatest things we’ve achieved in this country have been called absurd and ridiculous and outrageous at the time.

“We went to space. We finally got rid of slavery. We finally got black folks and women the right to vote. Those things were ‘crazy’ at the time,” Jayapal said. “If providing health care to every American is crazy, call us crazy.”

When he told Congress and the country in his State of the Union speech that “we are alarmed by new calls to adopt socialism in our country,” Trump was simply running with a line that was first tried out by Schultz. Besides blasting Medicare for All as “un-American,” the possible independent candidate labeled Warren’s proposal to slap a 2 percent tax on household net worth above $50 million and 3 percent above $1 billion as “punishing people.”

Then again, Schultz is a little touchy on the subject. He doesn’t think billionaires should be referred to as “billionaires.” He prefers “people of means” or “people of wealth.” He assured an audience at the San Francisco Jewish Community Center last week that he’s a self-made guy who grew up in a housing project in Brooklyn. But that’s not enough to make him want government to become more involved in health care delivery or college tuition or green jobs.

Trump’s socialism dig the other night earned a standing ovation from Republicans and a few red-state Democrats such as Montana Sen. Jon Tester. But “socialism” doesn’t pack the same sting in an era when Sanders and New York Rep. Alexandria Ocasio-Cortez can get elected by identifying as democratic socialists.

Call someone born after the Cold War a socialist, and they’ll shrug. They came of age during the great recession, when capitalist institutions were on the verge of collapse. Doing something about public-university tuition that tripled in the past 30 years sounds OK to people carrying six-figure debt from their student days. As for single-payer health care, an Associated Press-MTV survey last fall found that 69 percent of respondents under age 34 support it.

Another survey, this one by Harvard University’s Institute of Politics, found that 39 percent of voters under 34 don’t care if a candidate identifies as a democratic socialist, and 1 in 4 said it would make a candidate more appealing.

And young voters are fired up. A new study by Sacramento data expert Paul Mitchell found that turnout by young voters last fall in California soared to 46 percent of those eligible, up from 16 percent in 2014.

“The initial ‘wave’ election we just saw,” Mitchell wrote, “could be a precursor to a larger swell of voter turnout and engagement than we have seen in California.”

Such voters are looking for the type of bold changes Jayapal is backing. In 2016, she was one of the first legislators to support Sanders. She is uncommitted for 2020.

“There is no savior for the Democratic Party or for America,” Jayapal said. “What we need are people who are bold, who are listening. We want people who are not going to back down in the face of powerful interests. Because that is what we’re facing.”

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