Ordinary Americans have an opportunity — really, an obligation — to force this debate to occur. “This is now a big enough issue that I think people should actually become politically active and let their congressmen and senators know how they feel about this program and how they think the financial shortfalls should be filled,” said Alicia Munnell, the director of the Center for Retirement Research at Boston College. “I cannot think of a more serious problem going forward than the fact that benefits might have to be cut by 25 percent if we don’t have some political action.”

Professor Munnell, an assistant secretary of the Treasury and member of the Council of Economic Advisers in the Clinton administration, says Social Security should be repaired solely by increasing tax revenues — not by cutting benefits, which, she says, most Americans simply cannot afford to lose.

Mr. Simpson, on the other hand, says a combination of tax increases and benefit cuts are needed, though says this solution isn’t popular. “Everybody and his brother will jump all over you,” he said. “I’ve been there!”

Along with Erskine B. Bowles, President Bill Clinton’s former chief of staff, Mr. Simpson headed a commission appointed by President Barack Obama to find bipartisan solutions to the budget deficit, Social Security and other problems. The 2010 report of the Simpson-Bowles commission, “The Moment of Truth,” still makes interesting reading. But neither Democrats nor Republicans embraced it. “The politicians didn’t want to touch it,” he said. “They didn’t want to make the hard decisions.”

But, he said, a full-blown crisis has drawn close enough to make it worth the effort of trying to force the political class to play close attention.

Ask your elected representatives what they intend to do about Social Security, he said, but expect to hear something like this: “No problem, we’ll fix it, don’t worry, there will be no benefit cuts.”

When you hear that kind of thing, he suggested, you should respond forcefully. “You should say, ‘Sir — or ma’am or whatever — with terminological exactitude, you are a lying sack of’” — well, you get the idea.