Palin was a Hail Marry that missed. McCain was in deep trouble and needed someone to get the Fox News wing of the party excited. If you look at the polls from the time his numbers actually went up after he picked her. I think McCain over estimated her ability and underestimated the level of rabid hatred the media would focus on her. I can't really blame him for that she was a very popular governor with pulled herself up by her boot strap story. I don't think most people realized how far down the rabbit hole the media was willing to go to elect Obama but sweeping "God Damn America" Reverend Wright under the rug should have been a clue. The reality is the Palin Derangement Syndrome has as much to with the way she dressed and the way she talked as did with what she actually said. Hard to feel superior if you don't keep the White Trash in their place.
The RINO hunters (who in reality are the ones who are Republican In Name Only) hate McCain. McCain compromises and works across the aisle with the enemy. Since the average RINO hunter hates the government (except for the parts that help them) they have no problem with endless gridlock and nothing getting done. McCain also wants comprehensive immigration reform and anything short of a forced roundup of all illegals (preferable with the judicious use of cattle prods)is grounds for being labeled "no better that Obama". Their ineffective flailing and misdirected rage is the reason Trump is so popular now.