Part I: 100% of Social Security income should be taxable for those whose AGI would otherwise exceed $200,000 (couples) and $225,000 (singles).
Part II: Restructure Social Security payroll taxes both to raise the ceiling and introduce a progressive rate schedule as follows:
$1-50k-----11%
51-75k-----12%
75-100k---13%
101-150k---14%
151-200k---15%
201-250k---16%
251-500k---17%
Why is this important?
I am on Social Security, which borrows tens of billions every year from the U.S. Treasury to feed current retirees like myself, and which will not be around for my grandchildren unless it raises more of its own revenue and limits deductibility for high income retirees. As a benchmark, remember that the current rate is a flat 15.3% for all payroll income up to $110k, a very regressive schedule.