I've been hearing some Republicans bemoan the fact that Rumsfeld waited to announce his resignation until after the election.
What they're forgetting is that American politics don't happen in a vacuum. Sure, having Rumsfeld step down would probably have helped us with a few voters, but the reason Republicans in the field didn't vote for Republican's in the elections is not really that the war was going badly; it's more that the Republicans in office have failed us on domestic matters. Letting Rumsfeld go would not have fixed that problem.
Rumsfeld's resignation also signals something else, to everyday Republicans, and to our enemies abroad. "We're weak." (I don't think this is true, but that is how the terrorists will try to play it off, in fact they have already.)
The effect on voters in America would have been negligible. The effect on the terrorists would not have been. If Rumsfeld had resigned two months ago, the terrorists would have had a chance to crow about it, a chance to declare it a victory for them. It would have been reported as a sign that America was leaving the battlefield in disgrace. That none of these things would have been true doesn't matter.
With all that negative news (especially with news of the a renewed series of attacks in Iraq due to a renewed sense of hope), we would have lost the election solely because of Iraq. We might have, as you said, kept the Senate, but we would have still lost the House. And that, coming less than two months after the resignation of Rumsfeld, would have been seen as yet another victory for the enemies of America, yet another sign that Americans are weak and cowardly.
The two events (Democrats wining the election, and Rumsfeld resigning) give the terrorists cause to celebrate. However, instead of giving them two victories, Bush only gave them one. Instead of two separate boosts, they only get one. One point is just a dot on a plane, two points make a line, a trend, and that perceived change of momentum would have caused lots of problems for us. Bush also signaled that he's willing to work with the Democrats, gives the DD a new set of fresh eyes (and a set of eyes that has seen insurgency tactics before, something that is obviously useful now), and he gave the democrats a challenge. In effect, he said, "I'm willing to work with you as long as you give me what I need to do my job to keep America safe." Or, I'll get rid of Rummy if you give me Gates without any trouble, and we'll see where we can go from there.
We'll obviously have to wait and see how things go, but I think the resignation of Rumsfeld was played in a decent way. It's a natural time for a shake-up, and we've seen the Rumsfeld resignation coming in one way or another for a long time. This way, we limit the damage it does to us, and Bush gets to send a balloon up to the Democrats to see how they're react to a more Uniter-type policy.
Just another silver lining (though admittedly a thin one) that I'm seeing this week.