Nicole Gaudiano and Nicole Gaudiano | USA TODAY

Jack Gruber, USAT

WASHINGTON — Sen. Bernie Sanders, speaking at a policy forum here Tuesday, identified a singular roadblock to achieving success on a host of progressive policies — and it wasn’t the Trump administration.

It’s American oligarchy.

Re-framing a familiar theme from his 2016 presidential campaign in stark terms, Sanders on Tuesday argued that the small number of multi-billionaires who now have power over the country’s economic, political and social life is “one issue out there which is so significant and so pervasive that, unless we successfully confront it, it will be impossible to succeed on any of these other important issues.”

The solution, he said, is not only ending voter suppression, “extreme gerrymandering” and overturning the Citizens United Supreme Court decision, which helped pave the way for super PACs, but moving toward automatic voter registration. He called for Wall Street, billionaires and big corporations to start paying their “fair share” in taxes, and for “substantially” increasing the estate tax.

Echoing his 2016 stump speech, the Vermont independent said, “The American vision of the future, our vision, must be to create a government and an economy that works for all, not just a handful of billionaires.”

Sanders hasn't said whether he'll run for president again. He was among several possible 2020 presidential candidates, including Democratic Sens. Kirsten Gillibrand of New York, Cory Booker of New Jersey and Elizabeth Warren of Massachusetts, who spoke at the annual conference hosted by the left-leaning Center for American Progress.

The event was billed in part as an opportunity for speakers to “preview and sharpen the best arguments for rejecting far-right conservatism and for enacting progressive policies” at all levels of government.

Several spoke in favor of early childhood education, gender pay equity and family leave, raising the minimum wage and policies that recognize the dignity of work. But Democrats are still finding their way after losing the 2016 election to President Trump, with progressives continuing to battle establishment Democrats on policy ideas and messaging.

Brad Bannon, a Democratic pollster and consultant, said the question for some Democrats is how far they’re willing to go to match Sanders on policies he supports, such as a government-run, single-payer health care system or his forthcoming proposal to guarantee jobs for all Americans — policies primary voters support.

Booker, for instance, announced a “federal jobs guarantee” bill last month that would create a pilot program. He joined Gillibrand, Warren, Sen. Kamala Harris, D-Calif., and others in cosponsoring Sanders’ single payer bill last year.

“They’re really under a lot of pressure because Bernie is basically blazing the path and saying, ‘This is where we should go,’ and most Democratic primary voters think this is right,” Bannon said. “But a number of Democrats are afraid if they do a full Bernie, it will make them less likely to beat Trump in 2020 in the general election.”

Sanders, who is up for re-election this year, has been campaigning for other 2018 candidates in Arizona, Illinois, Iowa, Maryland, Pennsylvania, Wisconsin. That may help those candidates, not necessarily with establishment Democrats, but with the activist base, said Neil Sroka, communications director for the progressive Democracy for America.

“The mere act of securing a Bernie Sanders endorsement says something about your campaign and the values that you represent in a way that is exceedingly clear,” he said.

America Rising PAC, a GOP opposition-research group, says in a blog with a picture of Sanders that 2020 contenders are making promises they can’t keep.

“The leadership vacuum at the top of the Democratic party is pulling potential 2020 candidates to the furthest reaches of the progressive base,” Alexandra Smith, the PAC’s executive director, wrote in an email. “Message testing this year to prove their liberal bona fides will only muddle midterm prospects as Senate incumbents, in particular, attempt to present themselves as moderates in red states.”

During his speech Tuesday, Sanders called for progress on a single-payer program and tuition-free college, and a number of policies the other senators addressed, including raising the minimum wage, “equal pay for equal work,” protecting abortion rights, rebuilding the country’s infrastructure, criminal justice and immigration reform.

But he said the current “grotesque level” of income and wealth inequality is immoral and causing “massive suffering.”

He pointed specifically to Amazon founder Jeff Bezos, whose wealth reportedly increased by $33 billion in four months.