They already are. They're calling it Quantitative Easing. All they're doing is kicking the can a little further down the road.

There's a general agreement by economists, that as long as it is possible, countries will inflate their money supply (print money) rather than default of their debt. It amounts to much the same thing, because you're getting paid back money that is no longer worth anything. At the point where printing money ceases to be a viable option, the country will default.

The US case in particular is a lot more difficult to judge though, as CW said they're the world's reserve currency (which basically boils down to meaning that oil is sold is US dollar contracts globally, so all other countries must buy US $ so that they can use it to buy oil). China also holds $1.1 trillion in US debt, and Japan holds $890 billion. So for the US to blatantly inflate it's money supply, or default, will get China angry. As China is currently the ascending superpower, while the US is gradually declining, within a couple of decades the power balance in the world could be very different, and the US is likely to find itself with much lower living standards over all. But really it's such a huge, massive issue that no one is really sure how it'll all play out.

http://www.treasury.gov/resource-center/data-chart-center/tic/Documents/mfh.txt

Counterpoint: the Ryan budget.