Enemies of Bush criticize him for [some action], but if he'd [taken some alternative action], they'd criticize him for that too! Therefore, the criticism is invalid.It's true that there are people who will criticize any action taken by someone they don't like. They see inadequacy first and find the justification for it later. Pointing that out is essentially an ad hominem attack, and it doesn't make their criticisms invalid. The (supposed) irrationality of your opponent doesn't prove your own rationality.
Here's a hypothetical. Bush has a choice between torturing people or not protecting the country. (This is a false dilemma, but pretend it's not, for hypothetical purposes.) I think it's reasonable to criticize him for not protecting the country. I also think it's reasonable to criticize him for torturing people. Answering either of those criticisms is not a matter of pointing out that I'd criticize both choices. To answer the criticism, you have to show that (1) those really were the only options available, and (2) the option selected was the better. In the (simple) hypothetical situation given, even that is hard because the judgment eventually comes down to values (human rights versus national security) on which people can fundamentally disagree.
I think this kind of argument often makes a different mistake as well, and that's taking members of a group as a whole. (I think of this as similar to outgroup homogeneity, a fancy way of saying, "people who are not my friends are all the same.") They see Alice criticize Bush for doing too much. They see Bob criticize Bush for doing too little. They conclude that "Bush's critics" are inconsistent, even though the individual critics may be completely consistent.
I feel better now. Straw man target practice is always comforting.