Could Mccain actually be a democrat?

I was just reading on how he proposed a economic plan that was not welcoming to Republicans. They claimed they would not approve a plan that favored the democratic plan. Not to mention his plan included 70 1/2 year old retirees liquidate their pensions on their 70th birthday. Republicans said they will not back his plan. I honestly think the man thinks like a democrat , but calls himself a Republican. Why won't Republicans back him...maybe he has to much humanitarian in him?