If Obama had to face any real Conservative instead of a Moderate like McCain he would not have won. McCain was hand picked by Democrats who crossed over to vote in Republican Primaries to make sure it was McCain. However, these were Hillary supporters. That cost her the early Primaries and gave Obama a foothold. Had they not done that, the race would have shaped up to be Hillary Clinton against Mitt Romney.
How that would have turned out is anybody's guess.