I would appeal to simple reasoning: everybody has known that the U.S. is on an unsustainable spending curve due to entitlements for the last decade or more. The only thing that changes is how politicians choose to spin it from year to year. If you create a system where politicians get elected promising to spend money that doesn't exist, then such a system will outgrow any amount of revenue you can throw at it. If you somehow changed the rates right now and squeezed enough out of the economy to make it all balance? Ten years from now some new bunch of guys will be running on a platform to provide SUVs in every driveway or something equivalently intellectually sexy and emotionally attractive. It's simply too enticing not to.

But you asked for something solid, so here's the result of some random Googling. Note that it's a little unfair for this author to use the current year's deficit in this calculation, but then again with growth rates where they are it's only a decade or so until such spending will be commonplace even in a frugal environment.

http://billwhittle.net/?p=562

There are about 400 billionaires with a total net worth of around $1.3 Trillion.

Seriously, this entire discussion all boils down to how honest you can be about how the system is broken, not which party is to blame, how much the rich should pay, whether or not we need more or less government, or any of that. All of that nonsense is just bullshit to keep you coming out to vote.

I'd also point you to a graph of total debt as a percentage of GDP. http://www.usgovernmentspending.com/federal_debt_chart.html Even if you argue that the last year or two is somehow "special" (A common theme when its your guys spending the money) It's plainly clear that the trajectory leads to default in a very short amount of time.