What happens if we cut Social Security benefits for future retirees? Jed Graham does the math at Investors Business Daily:

Among retirees 80 and up, 54% count on Social Security for at least 80% of their income.

Further, even before benefit cuts, Social Security will only replace 36% of pre-retirement income for an average earner once the official retirement age rises to 67 in a decade — about half of what financial planners recommend.

The risk is that far too many Americans won't increase their savings to make up for cuts to Social Security. Working longer could help overcome benefit cuts as well, but that's no sure thing, as the Great Recession has shown. Health can also shorten careers, and while disability benefits can help, an average earner who becomes disabled at 62 would still face a 17% lifelong benefit cut under progressive indexing.