I am a Tea Party republican, and I think any Tea Party candidate should make a pledge to support the best man standing when the primaries are over. Same thing for the establishment republicans. If McConnell really said this, it was stupid. No candidate needs to wage war on his own party members, no matter what the circumstances. Whoever wins those primaries is going to need the support of the losers fans, so it is not just etiquette, it's good competition.
I held my nose and voted for McCain when I had to, and he's about as useless a republican and you can find.
And just for the record, those republicans who stay home from the general election because their guy lost the primary and just to prove how pure their patriotism is, are a lot worse than McCain.
Politics is a team sport, and you don't quit the team just because your favorite pitcher isn't on the mound.
A lot of republicans need to grow a pair and stand up for the ENTIRE team, not just for their favorites.