[alex_stoddard]

Maybe for an independent investor. But how can a t-bill be an investment for the government itself?

I am naively assuming that what backs the value of a t-bill is the US government's ability to accrue future tax revenue to pay it back.

What is it that makes a t-bill owed to Social security an investment rather than a tax deficit when it comes time to cut a social security check?

[jbooth]

What backs a t-bill is the "Full Faith and Credit of the United States Government". Along with smaller amounts of gold, it's the foundation of most countries' national reserves, yes, "most", notably China. If the US gov't defaults, social security getting paid back will be the least of our worries.