Because he’s lost the support of Elizabeth Drew. How can you possibly win the White House without the blessing of Lizzie Drew, who could give clinics at the Columbia Journalism School on how to write boring election chronicles!
Her complaint? McCain is--gasp--a Republican after all:
McCain’s caving in to this “compromise” [over Guantanamo] 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.
Keeping faith with the conservative base--the one unpardonable sin inside the Beltway. At least it is proof that it is possible to "shrink" in office (i.e., move to the right, as opposed to "grow" in office, which is WaPo-speak for "move to the left.")