A stealth Social Security cut!
Changing the inflation calculation for Social Security benefits from CPI to chained CPI is a benefit cut by stealth. Using the low inflation number would result in slightly smaller Social Security benefits every year. While the cuts would take place in small yearly increments the cumulative effect would be that over a seniors lifetime they would get tens of thousand less from Social Security (PDF).
Democrats in Congress fought fiercely against just this change, back in the Bush days, when they still were determined to protect SocSec.