The answer is you have to do some very, very dramatic things. We reduced the growth of Social Security to the level of benefits that could be financed by the payroll tax structure and moved the full retirement age by five years. We dramatically reduced replacement rates -- benefits to earnings late in life, although we didn't reduce anybody's benefits below the purchasing power [inflation index] except for the most affluent.

On health we chose to slow the rate of growth of health costs ... Not speaking for the committee I think the only way to do it is to put Medicare and Medicaid on a fixed budget. That would require vouchers based on income for Medicare that could vary by geography and health. In any case we're talking about something very severe. Then with all other speding, we squeezed defense so that they couldn't invest in new weapon systems but could retain their personnel. You could have minor foreign interventions but nothing on the scale of Iraq and Iran. On infrastructure and reserach we also clamped down on. These are the draconian changes on the spending side if you keep taxes where they are.

A lot of Republicans -- and some Democrats -- are calling for even more tax cuts across the board for extended periods of time. But this budget picture is dismal enough already. Did you consider what it would look like with even fewer taxes?

The thought of actually cutting the tax burden is really quite implausible.

Now tell me what a reformed budget would look like if politicians decided to keep spending stable and make all the reforms on the tax side.

At the other end of the spectrum, we said let's keep our promises to Medicare, Medicaid and Social Security while keeping the 60 percent debt-to-GDP figure. The tax increases are quite extraordinary.

We had two strategies for financing the package. We increased all rates proportionally -- including capital gains and the AMT -- until the top [marginal income tax] rate rose to 50 percent [from 35 percent, where it is today]. We did that for around 2020. At that point we introduce a VAT [value added tax, or consumption tax], first at one percent and growing to 8 percent by 2040. It had to grow fairly rapidly. For Social Security, we had to increase payroll taxes from 12.4 to almost 15 percent. And then we needed a surtax on top of all that. All this would take us from a total tax burden including state and local from below OECD average today to where by mid century we'd be considerably above average. Spun out to 2060 we'd be one of the highest tax burdens in the world right alongside Denmark and Sweden.

The other approach was to radically reform the tax system, getting rid of all tax expenditures [such as tax exclusions for employer health care and pension contributions ... see more here] like capping the employer health exclusion. It's really, really remarkable how much money you get back from tax expenditures, especially from capping the health exclusion. We could actually lower rates over time with that solution to the situation, while keeping the overall tax burden the same.