Kevin Drum's two-step plan for putting Social Security into long-term actuarial solvency is to first raise the payroll tax cap so it once again covers 90 percent of taxable payroll and second to slightly reduce benefits across the board by switching to the Chained Consumer Price Index for doing cost of living adjustments.
I did a Chained CPI explainer piece last week, and I'll just say the bottom line is that it's a mistake to regard this as some kind of technical fix. It's an across the board benefit cut, with the cuts falling especially hard on people who live a very long time. These things happen sometimes in life and it's all got to be part of the political mix. But I'll say this. If I proposed cutting Social Security benefits for the poorest retirees and cutting them especially severely for very old poor retirees, I don't think liberals would be enthusiastic. But C-CPI-U does just that. The fact that it also cuts benefits for not-so-poor seniors doesn't really make that any better. It's perfectly possible to design a Social Security plan that does CPI chaining and also boosts benefits for classes of seniors who are most vulnerable—check out Christian Weller's plan if you're interested—but at the cost of creating a situation where you can't describe the plan in two bullet points.
Long story short, I don't think Social Security ought to exist in some separate mental category from the whole rest of public policy. If spending must fall then spending must fall. But protect the poorest who need the money most.