But what’s talked about less often is how changes in our current borrowing costs are likely to affect our future borrowing costs in a self-perpetuating cycle. If our debt service goes from 7 percent of spending to 15 percent of spending, that makes our government debt a bigger risk for the same reason that a $1,000-a-month minimum credit-card payment is a very big deal for a man making $2,500 a month but not for one making $25,000 a month. How do lenders respond to greater risk? By demanding higher interest payments, usually. And those higher interest payments would raise our debt-service expenses as a share of federal income — and further erode our credit position, leading lenders to ask for even higher rates, etc. That’s the potential vicious cycle. That’s a recipe for a credit crisis that would make 2008–09 look like a picnic.

Hold on with the Chicken Little stuff. I’m not saying this inevitably will happen. I’m not even saying that it is very likely to happen over the short or medium term. Bond investors certainly don’t think it is likely, otherwise they’d already be asking for higher interest rates or moving their money to safer investments. What I am saying is that this is a risk, one that should be accounted for in our politics and understood in our debate about the debt and deficits, including in our debate about the current tax-cut proposal. Adding to the deficit adds an unnecessary risk — and avoiding unnecessary risks while working to minimize the risks we do have to take is what once was meant by the word “conservative.”