Donald Trump is on to something questioning why the federal government taxes Social Security benefits.

Technically, this isn’t even a tax on benefits. We already impose a tax on additional income that Social Security beneficiaries earn while they collect Social Security checks. If Social Security is the only source of income, then individuals don’t pay any tax on it.

As a result of this tax and other penalties, seniors who continue to work often pay the country’s highest tax rates—much higher than the rates young people with the same income pay. That’s unfair and a punishment for those who work while they collect Social Security benefits.

On the other hand, as others have pointed out, completely eliminating the tax would cost the Treasury large revenue losses at a time when deficits are already exorbitant.

However, there is a way to reform some of the worst features of the tax at low cost.