She's just woefully out of her depth:
Palin’s debate prep was going miserably, to the point where Schmidt had to peel off from McCain (who was having his own challenges responding to the financial crisis) and join Nicolle’s husband Mark Wallace in simplifying Palin’s prep so as to avert catastrophe...I’m sympathetic to Eskew and Wallace, and not just because they’re decent people. They’ve held their tongue from leaking what a couple of McCain higher-ups have told me—namely, that Palin simply knew nothing about national and international issues.
She is simply unqualified. To a certain extent, of course, her ignorance is her responsibility, but it's damning to McCain that he so cynically and irrationally picked her.
And then he turns into a bigger asshole:
I’ve heard from one well-placed source that McCain has snubbed her on one long bus ride aboard the Straight Talk Express, to the embarrassment of those sitting nearby. It has surely been implied to the governor that she should be eternally grateful to have been plucked from obscurity. And yet the high water mark of John McCain’s campaign for the presidency unquestionably began on September 3, when Palin gave her nomination speech—and ended precisely twelve days later, when McCain went off-script—I have that on the authority of the person who participated in the writing of said script—and told an audience that he still believed the fundamentals of the economy were strong.
This fits right into the accurate narrative of McCain. He is ALWAYS the honorable one, all errors cannot be made by him, because he views himself as the embodiment of all that is true, honorable, and correct. All things at variance with this are viewed with disdain. When Sarah Palin turned out to be unqualified and an embarrassment to him she gets shunned and the knives come out.
Even though it is all due to him, it's never his fault, but hers.
When you hear how "arrogant" Obama is, keep that in mind and tell me who the arrogant one really is.