Why was Rumsfeld fired?

Rumsfeld's defenders posit a theory of his firing in this morning's NYTimes: President Bush did not fire Rumsfeld because of any judgement about capability in his job, but instead because of his political liability in dealing with a Democratic Congress.

He was not surprised by President Bush’s decision to replace him the day after the midterm elections, several current and former aides said. He and Mr. Bush had talked several times about whether Mr. Rumsfeld could still operate effectively, especially if the Democrats took control of both the House and Senate, they said.

This defense does match the facts of the "day after the election" firing, and, apparently, no major changes coming in Iraq policy. I guess we'll have to wait and see whether Gates represents real change or just a new face.