From the comments
On your 2010 R&R post: Your point about 90% being neither sacred nor stable shows how badly many people misinterpreted the paper.
You also said we don’t know how much higher than 90% we can go. I’m not sure exactly what you meant, but I’ve suggested that the threshold we should be most concerned about is the point beyond which you can be sure you’ll never get back to safe debt levels, because you’ll be faced with the Catch-22 of both austerity and “not-austerity” pushing debt higher for different reasons. This threshold is much lower than the point at which large countries will actually experience a fiscal crisis and probably lower than most people think. A reasonable estimate is only 150% debt-to-GDP, based on the observation that there are no historical episodes of countries recovering from 150%+ that are at all relevant to the U.S. or U.K. today (yes, I used the R&R data among other sources to test this).
The risk that the U.S. sails through such a threshold is becoming very real at current debt levels.
If you (or anyone) are interested, my paper reviewing all historical episodes of debt >150% of GDP (from the R&R database) was posted last month on Seeking Alpha and on http://www.cyniconomics.com and it’s called “Answering the Single Most Important Question in Today’s Economy.” And if the U. Mass. trio are interested, I’ll even offer my calculations.