Yglesias is right that someone in the GOP, and not one of the usual "mavericks" like McCain, but someone, as he says, "awful" like the Senate's evil little troll Jeff Sessions, is going to have to come right out and say that the Iraq is FUBAR and it's all the Bushies' fault.
Sadly, I just can't see it happening. Over the past 4 years the GOP has transformed itself from the party of "anti-Clinton" to the party of George W. Bush. He has become the personification of the party - it's become rather personality cult-like. Members of Congress are motivated by some combination of a desire to "do good" (as defined by them personally - this could include all kinds of bad stuff) and "get re-elected," with the latter one having a rather heavy weight. If they push Bush over a cliff, he'll bring them all down with him.
If the calendar said 2003 that scenario would be possible. But, I don't see it happening.
So, all they can do is... Clap louder!