Bush is going to have a hard time with this one. Democratic Congressman John Murtha is a cranky old cuss and, at least when I worked on Capitol Hill, was a reliable vote for virtually anything that the Republicans wanted to do on the military front. But he was not a stooge for the Republicans - he is widely respected as a voice for military issues by both sides. It is going to look both churlish and partisan to attack what he has to say, particularly given that he said it with such passion. He's kind of like a Democratic John McCain, but with even more moral authority since he isn't quite as relentless in his courting of the spotlight. When Murtha gets up to talk, people listen.
Scott McClellan did his best, I suppose in responding, but let's face it - even Grover Norquist might be tempted to snort privately in derision at the idea that Michael Moore and John Murtha inhabit even the same corner of the universe.
Of course, Murtha and McClellan both could do with a close reading of the real master of speeches on war:
Don't write 'em like this anymore