Does he? Maybe
Should he? No
McCain needed a game changer and Palin was a game changer. Perhaps picking Romney or Pawlenty may have gotten him closer, but he would not have won. He needed someone to shake things up, maybe he didn't pick the right person to shake things up but he picked someone who gave him a better chance to win.
Another person who was just as conservative but less eratic would have Tennessee Congresswoman Marsha Blackburn. She would have been far less damaging in the suburbs and just as successful at rallying the base.