Clinton has promised to maintain the existing system with some modifications intended to help widows and women. Sanders believes that future retirees should receive more generous benefits funded with increased taxes on the rich.
This debate is particularly relevant to Tuesday's primaries. Social Security is an important source of retirement income for black and Hispanic Americans, who make up a significant share of the electorate voting on Tuesday.
The racial disparity in personal retirement savings is wide and growing. In 2013, the average white household had $125,000 saved in retirement accounts, while the average black household had just $26,500, according to an analysis by the liberal Economic Policy Institute. This discrepancy has increased in recent years, since white savings recovered more quickly after the financial crisis in 2008.
It's almost a five-fold difference. The huge gap reflects the accumulation of all the inequalities that African Americans confront from childhood, in school and throughout their careers, which limit their opportunities to earn and to save. Black unemployment is typically twice that of white unemployment, so black workers draw fewer paychecks during their lives. While they are working, they generally make less money. Black men's weekly earnings were just 74 percent of white men's last year, according to the Bureau of Labor Statistics.
Hispanic workers appear even worse off than blacks, with just $17,000 in savings. The racial disparity means that black and Hispanic workers are especially reliant on other sources of income in retirement -- such as residential equity, pensions and, above all, Social Security.
"What really matters is Social Security," said the Economic Policy Institute's Monique Morrissey, an economist.
Sanders's plan would help workers with scarce earnings and savings by making their Social Security benefits more generous and by increasing the annual cost-of-living adjustment.
At the same time, his plan would help middle-class workers and young people. Social Security is running out of money, and the agency projects it won't be able to pay beneficiaries what they are owed starting in 2034. Sanders's plan would improve the program's finances, guaranteeing that all workers are paid in full through 2074, according to a recent analysis by Social Security's actuaries.
The wealthy would pick up the tab. Sanders would levy taxes of 6.2 percent on income over $250,000 in both salaries and capital gains.
Clinton has not given her support to such a broad expansion of Social Security, or put forward a plan detailing what changes she would make to the system or how she would pay for them. Broadly, she has said she wants to help widows and female retirees in particular. They generally receive less from Social Security because they spend more years out of the labor force raising children or caring for loved ones.
It's a particular problem for black women, who are strong supporters of Clinton (89 percent of black female Democrats cast ballots for Clinton in South Carolina's primary on Saturday). That's because Social Security offers spousal and survivors' benefits for retirees whose husbands or wives made substantially more than they did. Black women, however, are less likely to marry, and if they do, they are more likely to earn as much as their spouses. As of 2009, more than a third of black women in late middle age would be ineligible for these benefits in retirement, about twice the number of white and Hispanic women who would not receive them.
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