In the case of Bush, it has become clear that he was, as many Republicans claimed, very closely aligned with the Clintons ... so Republicans making such charges have been proven correct.
Do we really need to say any more about McCain?
As for Romney, however 'nice' the man may be personally, he wouldn't even take on Obama in one-to-one debate. It was an apparent lack of conviction to principles.
...the sentiment you're expressing shows just how the GOP is moving further right, though.
This idea that they have to fiercely hate all democrats and oppose them and resist compromise at every turn, in order to be a 'real republican', otherwise they're a "RINO" is a fairly new mentality that's developed over recent times and represents a shift away from the middle.
Rewind to the days of Lincoln, people from opposing parties would occasionally run on the same ticket as a showing of ability to compromise and work with everyone. It wasn't uncommon for members of congress (from opposing parties) to be friends outside of work...and it certainly wasn't uncommon for people to dissent among their own ranks if there was something they didn't like.
Now, McCain is a
sellout because he personal friends with Joe Biden.
Bush is a
sellout because he shook Bill Clinton's hand in public and hugged the Obama's at his father's funeral.
Romney is a sell out because he didn't yell and scream and smear Obama during their debates (apparently, "lock them up", "if it were up to me, they'd be in jail" is the way debates are handled now)
All of that doesn't prove that the GOP is going back to the middle...it proves that the base is shifting further toward the right-wing fringes and trying to oust the actual moderates of the party that were preexisting.
Merely having a connection with someone from an opposing ideology doesn't make one less committed to their own. I'm pro-gun...but I have friends that are anti-gun...I still talk to them and treat them with respect and hang out with them. That doesn't make me a sellout to my position (although, with the state of the rabid NRA...who knows, they might say I am)