Nicole Gaudiano

USA TODAY

WASHINGTON — Sen. Bernie Sanders and Hillary Clinton both say they want to expand Social Security, but the Democratic presidential candidates differ on how much.

Sanders, I-Vt., has introduced legislation calling for an across-the-board increase in benefits of about $65 per month for most recipients. He also would boost the minimum benefit and use a more generous index to calculate cost-of-living increases.

Clinton has proposed more targeted increases, primarily for women, noting the poverty rate among widows 65 or older is nearly 90% higher than for other seniors. Her proposal would boost survivor benefits and create a caregiver benefit for those who left the paid workforce to care for children, parents or ailing family members.

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Progressives have long called on Democrats to oppose any cuts to Social Security, and both candidates say they do. But one progressive group that has not endorsed either candidate is calling on Clinton to go further and propose broad benefit increases.

“It would be great policy and great politics for her to support expanding Social Security for all Americans, not just low-income women,” Stephanie Taylor, co-founder of the Progressive Change Campaign Committee, wrote in an email. “The majority of Democrats, Republicans and independents support this big idea."

Advocates of broad benefit increases are counting on the wealthy to pay more into the system than they do now. Sanders' bill, for example, would lift the Social Security payroll tax cap on earnings above $250,000.

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But the centrist Democratic think tank Third Way rejects the idea that all benefits can be preserved without big tax increases on the wealthy and middle class. It says the Sanders proposal would give more benefits to wealthy individuals than to the poor.

“Right now, Clinton is being safe,” Third Way co-founder Matt Bennett wrote in an email. “She’s avoided signing on to the ridiculous Sanders scheme to raise benefits for all — an idea that is a pipe dream and provides 5 times more benefit to the rich than to the poor.”

Nancy Altman, founding co-director of Social Security Works, wrote last month in a HuffPost Politics blog that it’s “preposterous” to say that Sanders would be “coddling the rich.”

Under Sanders’ plan, people with the lowest earnings would receive the largest increase in Social Security benefits as a percentage of those earnings, she wrote. Those who work a lifetime at low wages would not retire into poverty, and the purchasing power of their benefits would be better protected, she wrote.

“The only way to even plausibly make the case that the Sanders' proposal disproportionately favors the rich is to obscure the facts,” she wrote.

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About two-thirds of seniors rely on Social Security for most of their income and the average benefit is $16,092 a year, according to Social Security Works. But the program will hit a cash-flow deficit in 2019 and won’t be able to cover all of its obligations after 2034.

Republicans have proposed cutting benefits, privatizing Social Security and pushing back the retirement age, proposals that Sanders and Clinton both oppose. Sanders also has fought a proposal by President Obama to slow the annual growth of benefits, and Clinton has pledged to oppose reductions in annual cost-of-living adjustments.

Clinton put a finer point on her position on Friday after Sanders responded to — and challenged Clinton to respond to — a progressive campaign to get candidates on record opposing any benefits cuts.

“.@BernieSanders I won’t cut Social Security. As always, I'll defend it, & I'll expand it. Enough false innuendos,” Clinton tweeted.

The two candidates agree on the need to generate money to finance Social Security.

In addition to lifting the cap on taxable income above $250,000, Sanders’ bill would tax affluent households' investment income. The bill would extend Social Security's solvency for 40 years, according to an analysis by the program’s office of the chief actuary.

In 2007, Clinton opposed then-senator Barack Obama’s proposal to lift the cap on taxable income, calling it a tax increase on the middle class. But this year, her plan would ask the wealthy to pay more, including options to tax some income above the current cap of $118,500 and taxing income not currently taken into account by the Social Security system.

“Obviously, lifting the cap at some point or another is a very live possibility,” she said during a Des Moines Register editorial board meeting last month.

Bennett, of Third Way, said Republicans and Democrats will need to compromise or the system will collapse.

“When there is a commission and she’s president, she will find a way to live with some kind of cutbacks, just as Republicans will find a way to swallow some tax increases,” he wrote.

Americans strongly support Social Security and are willing to pay more in taxes to stabilize the system’s finances and improve benefits, according to a 2014 online survey of 2,013 Americans by the non-partisan National Academy of Social Insurance. But it's unlikely any sweeping changes would pass Congress.

Republicans could lose their Senate majority this election year, but they will almost certainly retain control of the House and are unlikely to support increases in Social Security benefits, said Cal Jillson, a political science professor at Southern Methodist University in Dallas.

If Clinton were elected, she might be able to push through modest increases in the early months of her presidency, assuming Democrats also win the Senate and come close to winning the House, he said. It’s less likely Sanders would be able to secure a "top-to-bottom" overhaul of the program.

“It would have to be a Democratic sweep of historic proportions,” he said.

Follow @ngaudiano on Twitter.