There's nothing preventing the ECB from printing money like mad, which the US is already doing. In fact, there appears to be some suspicion among bond traders that they are about to start doing so. And that has a lot to do with whether bond traders will buy bonds in a particular currency. Not getting paid back at all is one thing - getting handed a loss via currency deflation in comparison to either hard asset values (i.e. oil, wheat) or another currency is yet another.
Bond traders don't want to take a loss, and institutional investors can't afford to take a loss, so when you start printing money and inflation goes up, they demand much higher yields to compensate. So in the end, once debt gets to a certain level your access to borrowing is blocked regardless unless you have a current account surplus, which the US does not have and will not have for the rest of the decade.
If the US were paying 6% on its CURRENT debt held by the public (already issued debt), it would be paying about 4.6% of real GDP just for interest. (US current debt 10.3 trillion, US real GDP last reported at 13.352 trillion.) If the US racks up another 2 trillion in deficits over the next couple of years, and even if the economy grows 2% each year, our debt held by the public will be about 12.3 trillion and our real GDP will be close to 13.9, so 6% interest would cost about 5.3% of real GDP.
You can't run continuous deficits over the long run greater than the increase in your real GDP. That's math. It rules the universe. In fiscal year 2011 our deficit was 8.7% of GDP. Obama's jobs program would have required raising that to over 9% of GDP, which is why he ain't gonna get it and was basically greeted by laughter from Congress when he proposed it:
http://www.treasury.gov/press-center/press-releases/Pages/tg1328.aspxIn fiscal year 2012 we'll run a deficit over 8% of GDP. In 2014 we will not be able to run a deficit larger than 5% of GDP, so it's just about over for us.
You can believe the nonsense about CBs printing as an eternal deficit-funding machine, but it won't change reality. Any country can run high fiscal deficits for a few years, but then the country will be forced to change direction.
After the Italian losses, Mr. Market will not accept a US public-issued debt close to 100% of GDP without demanding either austerity (US no longer growing its debt relative to real GDP each year) or very high yields, which would force us within a year to stop growing our debt relative to real GDP each year.
That's why Spain just tipped over. It's not that they have high debt/GDP ratios right now, but they don't seem able to curb their ongoing deficits so in a few years they will be near 100%, and the markets won't take it. Further, they have a debt-loaded economy and they can't grow out of it by loosening.
The only time a CB with the ability and willingness to print saves you is when private debt (debt owed by companies and households) is very low, so printing money fuels very high economic growth - much higher than the inflation it causes. Because the US levered up so much in the last few decades, the Fed can no longer fuel very high GDP by printing money. And we have seen that. The Fed injected over 600 billion beginning less than a year ago, and got lower growth as a result due to higher inflation.
Krugman and all those agony-econocolumnists are dead wrong. What determines economic growth are debt ratios, not printing money or stimulus. If an economy is carrying high debt ratios in aggregate, then stimulus produces little expansion of real economy and printing money produces little expansion of the real economy, because too much of the income gains are siphoned into servicing debt.