In a press interview that was recorded a few nights ago and broadcast yesterday, Tim Geithner said the kind of thing you want to hear a Treasury Secretary say: the US will absolutely never lose its Aaa debt rating.

Insofar as debt ratings (from Moody’s or S&P for example) measure credit risk, Geithner is on solid ground. The US can not possibly default on sovereign debt, as a matter of law.  We’ll run the printing presses before we default.

That leads to market risk for US debt, as rates may rise with perceptions of higher inflation. But that doesn’t make sense for at least two reasons.

First, look at the world around you. The dollar has been getting stronger and will probably continue to do so. The US is still the location of choice for storing reserves.

Second, and this is speculative: I believe the US will find a pathway to fiscal discipline. I’ll writing here over the next few days about this, but in short, I think that we’ll find a way to put on the large tax increases necessary to fund a huge expansion in entitlement spending without blowing our fiscal position apart.

One way it might happen is for Democrats to give up the dream of nationalized health care and accept market-oriented reforms. In return, Republicans will give up on large cutbacks in Social Security and Medicare commitments.

There’s one very odd thing that we’ll have to consider if we move toward fiscal discipline: if we issue less debt, then what will the Chinese do with their capital-account surpluses? The standard answer is that they’ll start buying up companies and other assets in the US. There just might be enough political pushback against that to force the Chinese to revalue their currency instead.

But you know, those are all reasons for believing Tim Geithner. He’s not a guy who comes off as having independent force of will or conviction. He always seems to be giving out talking points, and to be carrying water for a president who shows no particular interest in what business needs to thrive.

Reasons are all well and good. But markets look for confidence builders too, and those come from guys with real personal force. If Hank Paulson had said something like “A debt downgrade will absolutely never happen in the United States of America,” you’d be a lot more inclined to believe him.