He is, however, an opportunist. And he uses Bush to get himself into the limelight.
That's a specious argument, seeing how Keyes has been politically active long before Bush was, himself, in the limelight. Keyes has been consistent in his praise and his criticism, as far as I have ever read.
As for the Duke University speech, if I remember correctly, he directly criticized the administration's clarity about their stated reasons for the war. That's hardly a trashing. In fact, I can cite for you several sources where Keyes clearly states the war was/is just (whether or not the article you read on the Duke speech made that clear--sometimes articles withhold that sort of information if it suits their ends). What Keyes said was something I had been thinking (and wrote on, in another forum) for some time before I read anything Keyes had to say on the subject. Tell me if I'm remembering the speech's topic incorrectly.
George W. Bush ran for Congress in 1977, long before anybody even heard of Alan Keyes.
I'd even venture to say that, considering who his father is, he's been politically active in one way or another all his life.
As for Keyes' saying good things about Bush, you'll have to point some out to me.
Is it in his "I'm Not a Bush Republican" speech, the one where he said
Many conservatives believe that the Clinton presidency was the most dangerous time we have faced, as Americans and conservatives, in the history of the country. I do not share this belief. Rather, I believe that we are now entering that most dangerous era. For the bullet you hear is not the one that kills you. Organized and conscious advocacy of the principles that have made American liberty possible since the founding is unlikely to die at the hands of an explicit and avowed enemy like Bill Clinton. It is actually more likely that conservatives will passively accept political euthanasia for their cause at the hands of someone we have too readily believed could be entrusted with its wise care.
Or maybe you meant this one:
I've been watching closely, and I have not seen a single serious Bush administration initiative that corresponds in reality to the agenda of liberty and of conservative principles.