Assets are for practical purposes means and when relatively comfortable retirees draw on SS/401(k)s it is income. There are broadly two choices for the wealthy retirees:
1. cut back on SS and other benefits you can afford out of pocket
2. tax your income higher
I would wager they would choose 1. To this group, the taxes hurt worse than the benefit losses
For poor retirees:
1. cut benefits
2. don't cut benefits
I would wager they would choose 1
The other two commonly suggested fixes -- tax the wealthy and broad tax increases -- also fail in my opinion. The holes we are talking about are in the hundreds of billions per year and won't be fixed by taxing just the wealthy. A broad middle class tax increase will also likely be rejected as unpopular.
It really is my belief that a slow-motion failure here is best. If any fix occurs as the social security trust fund is at 0 cash and while the bond market is in revolt, there will be no fiscal room to maneuver to raise cash from the debt which forces rationing.