Sen. Bernie Sanders has a plan for making Social Security solvent. As the program exists today, no dollar above $106,800 is subject to Social Security taxes. If we remove that tax ceiling, Social Security is basically fixed forever. Sanders' argument:

An individual who earns $106,800 pays the same Social Security tax as a multimillionaire. That's wrong.

It certainly seems wrong when you stop there. But Social Security isn't just a tax system. It's also a benefits system. An individual who earns up to the taxable ceiling will pay the same tax as the millionaire and receive the same benefit as the millionaire. Millionaires pay far less of their salaries into Social Security, and Social Security replaces far less of millionaires' salaries after they retire.

Moreover, unless we change the benefits structure, taxing millionaires up to their last dollar will mean including their last dollar in their retirement benefits. That means the federal government will be paying some multimillionaires with 401(k) plans the size of their private yacht tens of thousands of dollars a month for decades after they retire. That seems wrong, too.

Sanders continues:

According to CBO, applying the tax to all income would provide all the revenue that Social Security needs for the foreseeable future -- for our kids and grandchildren and great grandchildren.