Social Security is sound financially: True or false?

NEW YORK (CNNMoney.com) -- Since 1983, Social Security has taken in more revenue than it has needed to pay out in benefits.

That surplus revenue was borrowed by Uncle Sam and spent on other areas of the federal budget. In exchange, Uncle Sam promised to pay the program back with interest.

To date the federal government's tab to the program's trust fund has grown to roughly $2.5 trillion.

Starting in 2015, Social Security is projected to permanently take in less revenue than it has to pay out annually.

Those who say the program is nevertheless in good shape for years to come and shouldn't be a central part of any debt-reduction plan offer three main reasons:

Trust fund: The $2.5 trillion trust fund can ensure that the program continues to pay out 100% of promised benefits over the next quarter century.

U.S. backing: The promise to pay back the $2.5 trillion is backed by the full faith and credit of the United States, just like any bond sold to China or other investors.

Money maker: Far from contributing to the country's debt problems, Social Security through its surplus revenue actually made the federal deficits smaller than they otherwise would have been since 1983.

Those who say Social Security is in trouble financially offer two key reasons:

Empty coffers: To pay back that $2.5 trillion, the federal government will have to either borrow more, tax more or spend less. And that will put even more strain on taxpayers and the federal budget during a time of record debt.

Long-term shortfall: By 2037, the $2.5 trillion trust fund is projected to be tapped out anyway, at which point Social Security will only be able to pay out roughly 75% of promised benefits.

And here are some general points about the program that people on both sides of the debate seem to agree on, at least on days when they're listening to their better angels:

Gradual reform: Changes to close the program's long-term shortfall will be less painful and abrupt if they are implemented gradually.

Protect the vulnerable: Any changes agreed to should not affect current or soon-to-be retirees and should protect future retirees who are most vulnerable.