Why Biden, Republicans fought over Social Security at State of the Union

The most dramatic moment of Tuesday's State of the Union address came when several Republicans audibly booed President Joe Biden, with Rep. Marjorie Taylor Greene even shouting he's a "liar."

The cause of their anger: what he claims "some Republicans" want to do to Social Security.

Biden accused some in the GOP of wanting to make changes to the entitlement program, which 65 million Americans currently rely on, including putting the money spent to a vote.

Given how politically sensitive the subject is, the Republican pushback was swift, and Biden quickly turned the tables.

"So, folks, as we all apparently agree, Social Security and Medicare is off the books now, right? They're not to be touched?" Biden shot back. "All right. All right. We got unanimity."

The back-and-forth represented a debate Democrats and Republicans have been engaged in for months over Social Security, especially when it comes to government spending and the debt ceiling. Republicans have demanded spending cuts in exchange for raising the debt ceiling and avoiding default, but the party has not laid out exactly what cuts it wants.

Here's what Tuesday night's fight is all about:

What proposal was Biden referencing?

While Biden said in his speech he was "politely not naming" any one lawmaker, Sen. Rick Scott of Florida last year proposed "sunsetting" all federal programs every five years, unless Congress votes to renew them. Social Security would theoretically fall under that broad umbrella.

"Anybody who doubts it, contact my office. I'll give you a copy. I'll give you a copy of the proposal," Biden said to counter the shouts of "liar."

Richard Johnson, a senior fellow and director of the retirement policy program at liberal-leaning Urban Institute, said it's hard to imagine Scott's proposal would be "workable."

"It would certainly undermine confidence in the program," Johnson told ABC News. "It would really create a lot of uncertainty about people's retirement benefits in the future."

Do Republicans support Scott's plan?

The proposal wasn't exactly welcomed with open arms. Senate Minority Leader Mitch McConnell, R-Ky., was quick to call Scott's plan a "nonstarter" after it was released.

"We will not have as part of our agenda a bill that raises taxes on half of the American people and sunsets Social Security and Medicare within five years," he said at the time.

Scott defended his proposal on Wednesday, stating he doesn't want cuts to Social Security and that he "will not be silenced by the Washington establishment."

What have Republicans said about Social Security?

Andrew Biggs, a senior fellow at the conservative-leaning American Enterprise Institute, said while Democrats have been consistent in their views against cuts to Social Security, Republicans' positions are a bit murkier.

"That's simply because they're not speaking with one voice, and there's different views among Republicans both on the policy they would want and the strategy they would advocate to get to that policy," Biggs told ABC News.

Along with Scott's plan, Wisconsin GOP Sen. Ron Johnson had suggested making the program's funding discretionary rather than mandatory and up for approval every year. Johnson said the intent is to better track Social Security funding, but experts have worried it could subject the program to protracted budget battles.

The Republican Study Committee, which represents the largest group of House Republicans, previously called for raising the age for Social Security to 70 for younger workers and trimming auxiliary benefits for high-income earners in order to cut costs.

When the debt ceiling issue began, some Republicans seeking spending cuts proposed thinking about how Social Security -- which accounted for nearly 20% of federal spending, or $1.22 trillion, last fiscal year -- could be altered.

Where does Social Security stand in the debt ceiling debate?

House Speaker Kevin McCarthy, before Republicans won back control of the House, raised eyebrows when he told Punchbowl News in October he wouldn't "predetermine" whether reforming the entitlement program would be part of the negotiations.

But McCarthy's since said cuts to Social Security and Medicare won't be part of GOP demands in the debt ceiling talks.

"Cuts to Medicare and Social Security, they're off the table," he told reporters on the eve of Biden's State of the Union address.

What about the problems facing Social Security?

As the back-and-forth between Democrats and Republicans continues, Congress will eventually need to act on Social Security as it faces a long-term funding shortfall.

With more retirees taking out the system than there are workers putting into it, the Social Security trust fund has estimated that by 2034 it would be able to cover only 77% of scheduled benefits. They've asked Congress to address the issue before it gets to that point.

Possible solutions include raising the full retirement age, increasing the payroll tax, reducing benefits for higher earners and more. In contrast to GOP proposals, Democrats have so far generally coalesced around Social Security tax increases for the wealthy, while significantly increasing benefits.

"Congress has been a poor steward of this program, in the sense that they simply delayed acting on the solvency issue and it's clear they're delaying and for political purposes because they don't want to make the difficult decisions," Biggs said.

"But it can't kick the can down the road forever. And the longer you kick it down the road, the harder it gets."