Perot could run outside a party because he was incredibly rich and was not a recognized member of a party. McCain can not cause it comes across as soour grapes and he will get maybe 1% of the vote. Ask John Anderson about 1980 and what happens when a Republican Establishment type trys to run as a third party.
"Ask John Anderson about 1980 and what happens when a Republican Establishment type trys to run as a third party."
I know where you are coming from on this. However, this is not 1980 and the Right and Left are more defined. The middle of the road voters are faced with a "I want a strong defense, religion as well as more social awareness candidate.
If you think about it, that is where Hillary is trying to position herself and where people like McCain and Guiliani already are. What is scary is that you get a McCain, who can generate a lot of cash to do this and you have Hillary in the White House in 08.