Andrew Sullivan writes today, among other things:

In retrospect, the president should have clearly said last week that Lott should step aside as SML, which would have sped events up. I can see why he didn’t. He doesn’t want to interfere with the Senate’s business, he said the right thing about the underlying issue, and anything more might have seemed over-kill.

There’s another reason, I suspect.

The President has no direct power to remove Lott–that can only be done by his colleagues in the Senate. If he came out and publicly demanded that he step down, and Lott refused to do so, and the Senate refused to remove him, the President would have appeared, in the public perception, to be weak and unable to control events. I don’t think that he wanted to risk that, and perhaps he still doesn’t.