Dylan Matthews balances Social Security by lifting the contribution cap:
Currently, wages over a certain yearly total ($106,800 this year) are exempted from Social Security payroll taxes. Medicare's payroll tax has no such cap. This has raised the question of how raising the cap could extend Social Security's solvency....Congressional Research Service looked at this question in 2008 by evaluating three different proposals. The first would raise the cap so that 90 percent of wages are taxed (CRS estimates this would mean a cap of $171,600 in 2006) and pay higher benefits to those affected; the second would eliminate the cap and pay higher benefits; and the third would eliminate the cap for taxes but would not increase benefits...
While all proposals put a dent in the shortfall, completely eliminating the cap without increasing benefits actually creates a long-term surplus, and eliminating the cap while increasing benefits comes close. The nature of Social Security as a social insurance, rather than welfare, program suggests that the latter proposal may be more palatable, as it retains the connection between what wage-earners pay into Social Security and what they get out of it.
This is basically a big new tax on the rich. But it is also the closing of a silly loophole. In an ideal world, it would be unnecessary. Now, this reform, or something like it, seems to me to be essential.