I suggested elsewhere that McCain wins the nomination only if conservatives vote in the Dem primaries. That's one way to keep Hillary out of the White House.
McCain was also instrumental in that "Gang of 14" appeasement of the Democrats. The GOP had the House majority, but the Dems were allowed to control the judiciary process. McCain's compromise - which left intact the precedents that allowed the Dems to get away with that - lost McCain the Republican base forever.