If you've been paying attention to the 2020 presidential race, you've likely heard where many candidates stand on Medicare. Yet another topic — Social Security — has thus far been largely absent from the debate. Americans rely on Social Security benefits for income in retirement, in the event they are disabled and to help take care of their spouses and dependents.

All ten Democratic presidential candidates raise their hands to indicate that they would provide Medicaid benefits to illegal immigrants during the second night of the first Democratic presidential candidates debate in Miami, June 27, 2019. Mike Segar | Reuters

However the reserves used to partially fund the program are expected to be depleted in 2035, according to the latest projections from the Social Security Board of Trustees. At that time, the system will only be able to pay 80% of retirees' benefits if nothing is done before then. Social Security is a topic that should be addressed on the debate stage, said Nancy Altman, president of advocacy group Social Security Works, because one in four Americans receive support from the program and polls show many people are concerned about its future. "It would be a real public service and would help people decide who to vote for," Altman said. Here is what we know so far about where the key presidential candidates stand on this issue. The Democrats listed were drawn from those who ranked highest in a Quinnipiac University National Poll released on July 2.

President Donald Trump Zach Gibson | Bloomberg | Getty Images

President Donald Trump

"As President Trump has said repeatedly, he is committed to protecting Social Security," said Kayleigh McEnany, national press secretary for Trump's 2020 campaign. "He reiterated this promise yet again on June 24 in noting the great deal of time his administration spends on protecting Social Security," McEnany said. "Democrats, meanwhile, would have to make painful cuts to Social Security and other entitlement programs to pay for their $93 trillion Green New Deal and government takeover of health care." Congressional Democrats banded together last September to create the Expand Social Security Caucus following Trump's claims that the party will "destroy your Social Security." Supporters of expanding Social Security take issue with the $26 billion in spending cuts to the program that the president proposed in his 2020 budget. However, in a March press briefing, acting OMB director Russell Vought said the president is proposing reforms to programs that are "on autopilot" while at the same time protecting seniors by not changing Social Security or Medicare funding.

Democratic presidential candidate former Vice President Joe Biden speaks during the second night of the first Democratic presidential debate on Thursday, June 27, 2019, at the Arsht Center for the Performing Arts in Miami. Al Diaz | Miami Herald | Tribune News Service | Getty Images

Joe Biden

The former vice president's campaign seemingly has not taken a public stance on Social Security reform. However, in the past Biden has raised ideas including means testing for benefits, raising the full retirement age or increasing the cap on payroll tax earnings. Currently, employers and employees each pay 6.2% on wages up to $132,900. Biden spoke about Social Security in a May 2018 speech on the middle class and the economy at the Brookings Institution. "Paul Ryan was correct when he did the tax code, what was the first thing he decided we need to go after? Social Security and Medicare," Biden said in his speech. "Now, we need to do something about Social Security and Medicare. That's the only way you can find room to pay for it." In that speech, Biden said he doesn't know a lot of people in the one percent that are relying on Social Security in retirement. He called for a "pro-growth progressive tax code" and getting rid of loopholes like stepped up basis on certain assets. That would help raise revenue to "make sure that Social Security and Medicare can stay," he said.

Democratic presidential hopeful US Senator for California Kamala Harris speaks during the second Democratic primary debate of the 2020 presidential campaign season hosted by NBC News at the Adrienne Arsht Center for the Performing Arts in Miami, Florida, June 27, 2019. Saul Loeb | AFP | Getty Images

Kamala Harris

Harris, a California senator, teamed up with other senators earlier this year to introduce a bill aimed at expanding Social Security. Other presidential candidates supporting that legislation include Sens. Bernie Sanders (I-Vt.), Cory Booker (D-NJ) and Kirsten Gillibrand (D-NY). Among the features of that legislation, called the Social Security Expansion Act, include expanding the program's solvency to the year 2071, increasing benefits and cost-of-living adjustments, updating the special minimum benefit for low-income workers and adding student benefits for children up to age 22 of deceased or disabled workers. "We need to expand Social Security and provide our seniors and other beneficiaries of this vital program with greater dignity and peace of mind," Harris said of that proposal in a February statement. On June 29, Harris tweeted that as president she would oppose any cuts to Social Security and Medicare. Tweet

Democratic presidential candidate Sen. Bernie Sanders (I-VT) speaks in the second night of the first Democratic presidential debate on June 27, 2019 in Miami, Florida. Drew Angerer | Getty Images

Bernie Sanders

Sanders introduced the Social Security Expansion Act alongside Rep. Peter DeFazio (D-Ore.) in February. That bill has the support of other Democratic presidential candidates including Sens. Kamala Harris (D-Calif.), Cory Booker (D-NJ) and Kirsten Gillibrand (D-NY). The proposal calls for raising benefits by about $1,342 a year for seniors who make less than $16,000 per year. It would also make all income of more than $250,000 subject to the Social Security payroll tax. More from Personal Finance:

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This bill could extend Social Security's solvency for the rest of this century

Student debt forgiveness proposals likely to resonate more in blue states "It is time to expand Social Security, not cut it," Sanders said in a statement announcing the introduction of the bill. "At a time when more than half of older Americans over the age of 55 have no retirement savings, our job is to expand Social Security to make sure that everyone in this country can retire with the dignity they have earned and everyone with a disability can live with the security they need," he said. Sanders supports the same reform changes in his presidential campaign platform. Of note, Sanders is campaigning for the Democratic presidential nomination. He is not affiliated with any party in his role as senator from Vermont.

Democratic presidential candidate Elizabeth Warren gestures as she speaks during a campaign stop at George Mason University in Fairfax, Virginia on May 16, 2019. Mandel Ngan | AFP | Getty Images

Elizabeth Warren