It’s one of the biggest public-policy challenges facing the country. But the future of Social Security wasn’t mentioned in either of the first two presidential debates, and it might not come up in the final debate from Las Vegas, either.

If it doesn’t, it could be because neither Donald Trump nor Hillary Clinton really wants to talk about it.

Voters, however, do—and they seem to be deeply pessimistic. A sampling of comments WGBH News got from passers-by in Copley Square this week: “I hope down the road that it’s around, but with the [political] climate and the way our government’s working right now, it’s anybody’s guess.” “I think they’ll probably abolish it, or the funds will be gone.” “I don’t think it’s going to be around.”

Still, according to Boston University economist Laurence Kotlikoff, most people don’t really get just how bad the situation is right now.

“The Social Security system is bankrupt,” Kotlikoff says. “It’s not bankrupt in 19 years, when it will not be able to pay all the benefits according to the projections; it’s not bankrupt in 10 years. It’s bankrupt today.”

As expert assessments go, Kotlikoff's is somewhat extreme. Using an analytical method known as infinite-horizon budget accounting, Kotlikoff concludes that Social Security’s shortfall is about $32 trillion.

Some experts believe that number is far too dramatic – especially since, according to current projections, Social Security will be able to discharge all its obligations through 2033, and 79 percent of its scheduled payments through 2079.

But Kotlikoff says that whatever analytic technique you prefer, and whatever number it yields, the basic problem is inescapable.  

“We’ve taken money from young people, given it to old people, and said to young people, ‘Don’t worry—when you’re older, we’ll be able to take from your kids.’ But there aren’t that many kids, and they’re not earning that much.”

Substantially reforming Social Security has long been considered a third rail in politics. Which might explain why, so far, the two presidential candidates are talking about rather modest reforms that might actually create significant new costs.

Hillary Clinton wants to expand benefits for people she says are “barely making it,” including widows and individuals who left the workforce to become caregivers.  But while Clinton is promising more largesse, she’s against raising the retirement age. And even though she says the wealthy need to pay more, it’s not clear whether she’d lift the cap on taxable income.

For his part, Donald Trump has said he’ll “save Social Security” by bringing jobs back from China and Mexico—in other words, by making America great again.

Step two in Trump’s plan? Ferret out fraud that he thinks might be in the system.

“Like six million people are getting social security, they’re dead, meaning somebody else is picking up [the cost],” Trump said at a campaign event last year.

“The press is going to have to check” that figure, Trump added. “Because what do I know?”

What we do know is that paying more has limited appeal. In Copley Square, I asked a current Social Security recipient visiting from out of town if she’d be willing to pay more in taxes—or see other people pay more in taxes—to strengthen the system.

“No,” she replied with a laugh. It was a quick and honest answer.

For his part, BU’s Kotlikoff would like an honest answer from policymakers. Since he believes he hasn’t gotten it, on Social Security or other issues, he’s decided to run for president as a write-in candidate, with ambitious plans to overhaul Social Security.

“Freeze the existing system, and put into place a new personal-security-account system that does not involve any participation by Wall Street, but does involve… having a government return on your investment,” Kotlikoff told me.

It’s a proposal that might make economic sense—but is as improbable as Kotlikoff’s own candidacy.