This week's landmark tax deal sharply changes the financial outlook for Social Security. That has huge implications for your retirement. And most people don't have a clue what's coming.

The deal, by cutting payroll taxes for one year, weakens Social Security's funding. It puts those payroll taxes "in play" as a political football for the first time. And by freezing federal taxes at today's low rates, it will add at least $900 billion—and probably much more—to our spiraling national debt. That threatens the ultimate financial...