SAN FRANCISCO — Sen. Bernie Sanders’s California push for his plan to provide four years of government-paid college to all Americans underscored two themes of the Democratic primary contest: how much the party has moved in his direction since his first presidential campaign, and how that move has diminished Sanders’s once-singular hold on liberal positions.

Since 2016, when Sanders campaigned on providing free college — and expanded the impact this year with a plan to forgive $1.6 trillion in existing student loans — higher education affordability has become a key topic for most of the presidential candidates as they seek to attract younger voters.

Indeed, almost all the leading candidates now agree to offer at least two years of free college, as Sanders reminded more than 1,000 people gathered Friday near San Francisco’s Civic Center.

“Four years ago, when we talked about the idea [of free college] it was perceived by the political establishment and by the business establishment to be a radical idea. . . . That idea is becoming less and less radical every day,” Sanders told the crowd. “If we are to have the best-educated workforce in the world, we need to rethink what public education is.”

The plight of students and parents saddled with rising college costs has created some fissures among presidential hopefuls, broadly dividing liberal candidates who offer far-reaching proposals from moderate Democrats who support a more limited approach. 

Even those farthest to the left — specifically Sanders and Sen. Elizabeth Warren (D-Mass.) — are divided over the details of who should qualify for the federal programs.

But as with Medicare-for-all and other proposals Sanders has long championed, the issue’s growing popularity has given rise to broader support among his competitors, effectively giving voters more options.

As a result, some of Sanders’s former supporters have left for other candidates espousing similar ideas, including Warren, Sanders’s Senate ally.

“Now that 2020 candidates have adopted those proposals, he doesn’t seem as cutting edge as he was in 2016,” said Basil Smikle, a Democratic strategist and former executive director of the New York State Democratic Party.

Sanders and Warren have dived most deeply into the topic and share similar plans when compared with their more moderate counterparts in the 2020 race. But Warren’s plan includes several caveats. Student debt would be forgiven up to $50,000 for every person with a household income of less than $100,000, while those with income between $100,000 and $250,000 would have only part of their debt canceled. Sanders, in contrast, would eliminate all student debt regardless of income. Both favor free four-year college at public schools.

“Bernie will always propose a plan that addresses the full scope of the problem, that has a just frame for working people and holding corporations accountable,” said Josh Orton, national policy director for the Sanders campaign. 

As the candidates sell their respective policy proposals, many claim that their solution would alleviate the racial wealth gap. But economists are split over whether a universal elimination of student debt, like Sanders’s, or a capped approach, like Warren’s, would do more to address that inequality.

Critics of Sanders’s universal plan say that eliminating all student debt will disproportionately benefit wealthier, white families. But opponents of Warren’s proposal argue that adding qualifications could dissuade some of those who could benefit from the program to take part.

“It’s important to think about where your money is going. . . . [We] also want the money to be targeted to the people who need it the most,” said Louise Seamster, a sociologist at the University of Iowa who worked with a team of researchers from around the country to develop Warren’s student debt forgiveness plan.

The two candidates also differ in how they plan to pay for their respective plans. Warren has said her $1.25 trillion program would be funded through her wealth tax of 2 cents on every dollar of net worth    above    $50   million    and 3 cents   on    every    dollar   above $1 billion. Sanders proposes a tax on Wall Street speculation to fund his estimated $2.2 trillion higher-education programs.

“There’s a lot of different pieces of calculus that fit into just creating a budget estimate. It’s actually very difficult to do for any program that is related to student loans,” said Colleen Campbell, director for postsecondary education at the Center for American Progress Action Fund.

But the moderate competitors have offered more limited solutions, often with fewer specifics. South Bend, Ind., Mayor Pete Buttigieg — who has said that he and his husband owe more than $100,000 in student loan debt — supports free four-year public college for low- and middle-income families. He vows to “confront the student loan debt” but has offered no specifics. Sen. Kamala D. Harris (D-Calif.) supports debt-free four-year college and greater refinancing options. Former vice president Joe Biden has yet to offer a plan for student loan forgiveness or four-year college affordability.

At Sanders’s Friday rally, dedicated to the topic of college affordability, the issue was an urgent one for many attendees who said they were still paying the price for the decision they had made to attend college.

Anya Wayne, 43, from Berkeley, plans to attend divinity school, but she will have to take out loans to cover her living expenses. Though Wayne does not know how much debt she will accumulate, she assumes it may mean that she will never be able to buy a house or do much international travel. She considered abandoning divinity school altogether, but her dream is to become a chaplain.

Student debt is “changing the way that people go to school . . . decisions that people make in terms of their futures, limiting opportunities,” Wayne said. “Young people are drowning.”