When Bush, issued a “signing statement” in 2006 on McCain’s hard-fought legislation placing prohibitions on torture, saying he would interpret the measure as he chose, McCain barely uttered a peep. And then, in 2006, in one of his most disheartening acts, McCain supported a “compromise” with the administration on trials of Guantanamo detainees, yielding too much of what the administration wanted, and accepted provisions he had originally opposed on principle. Among other things, the bill sharply limited the rights of detainees in military trials, stripped habeas corpus rights from a broad swath of people “suspected” of cooperating with terrorists, and loosened restrictions on the administration’s use of torture. (The Supreme Court later ruled portions of this measure unconstitutional.)

McCain’s caving in to this “compromise” did it for me. This was further evidence that the former free-spirited, supposedly principled, maverick was morphing into just another panderer – to Bush and the Republican Party’s conservative base.

Other aspects of McCain, including his temperament, began to trouble me. He seemed disturbingly bellicose. He gave the Iraq war unflagging support no matter the facts. He still talks about “winning” the war, though George W. Bush gave that up some time ago. As the war became increasingly unpopular, he employed the useful technique of blaming its execution rather than recognizing the misconceptions that had led him to be one of the most enthusiastic champions of the war in the first place.

Similarly, in making a big issue of having backed the surge (and simplifying the reasons for its apparent success), he preempts debate on the very idea of the war. He has talked (and sung) loosely about attacking Iran. More recently, he oversimplified this summer’s events in Georgia and made intemperate remarks about Russia, about which he’s been more belligerent than the administration for some time. (He has his own set of neocons.)

There’s an argument that all this compromise wasn’t necessary: some very smart political analysts believed from the outset that McCain could win the nomination by sticking with his old self. And they still believe that McCain won the nomination not because he gave himself over to the base but as a result of a process of elimination of inferior candidates who divided up the conservative vote, as these observers had predicted. (These people insisted on anonymity because McCain is known in Republican circles to have a long memory and a vindictive streak.)

By then I had already concluded that that there was a disturbingly erratic side of McCain’s nature. There’s a certain lack of seriousness in him. And he does not appear to be a reflective man, or very interested in domestic issues. One cannot imagine him ruminating late into the night about, say, how to educate and train Americans for the new global and technological challenges.

McCain’s making a big issue of “earmarks” and citing entertaining examples of ridiculous-sounding ones, circumvents discussion of the larger issues of the allocation of funds in the federal budget: according to the Office of Management and Budget, earmarks represent less than one percent of federal spending.

Now he’s back to declaring himself a maverick, but it’s not clear what that means. If he gains the presidency, is he going to rebel against the base he’s now depending on to get him elected? (Hence his selection of running mate Sarah Palin.) Campaigns matter. If he means “shaking up the system” (which is not the same thing), opposing earmarks doesn’t cut it.

McCain’s recent conduct of his campaign – his willingness to lie repeatedly (including in his acceptance speech) and to play Russian roulette with the vice-presidency, in order to fulfill his long-held ambition – has reinforced my earlier, and growing, sense that John McCain is not a principled man.

In fact, it’s not clear who he is.

Elizabeth Drew is author of “Citizen McCain” (Simon & Schuster, 2002; paperback with new introduction, 2008.)