It will never get to 'reduced' benefits. What they are doing is not increasing the limits where taxes are taken from you benefits*. The current income limits have not been adjusted in years. So as people earn more and receive more benefits, more of those benefits will be taxed effectively reducing benefits.
There will also be slight adjustment like increasing FICA taxes, increasing the income limits on FICA taxes, and last but not least increasing retirement ages.
**"For individual (single) tax filers, if your combined income is between $25,000 and $34,000, 50% of your Social Security benefits may be subject to income tax. If your combined income is more than $34,000, up to 85% of your benefits could be taxable.
For joint filers, the income thresholds increase to a range of $32,000 to $44,000 for 50% taxation, and $44,000 and above for 85% taxation. Under no circumstances is more than 85% of your Social Security benefit subject to taxation, no matter how much income you have."