Andrew Sullivan has rounded up the response of various pundits
here. I think the best response is from Matt Yglesias:
There are two metrics to keep an eye on when assessing American debt. One is the interest rate the Treasury has to offer to get people to buy the debt. Currently that number is low. The other is the “spread” between bonds that are indexed for inflation and bonds that aren’t indexed for inflation which serves, among other things, as a gauge of market assessment of the risk that we’ll have no choice but to inflate the debt away. Currently that number, too, is low.
Smart People I Know 