True. The only way it actually happens in our system is when a popular candidate with one of the two main parties loses a primary and runs third party. Teddy Roosevelt with the Bull Moose (Progressive) Party taking more votes than the republican party, but still losing to Wilson. More recently, Lieberman in Connecticut, or possibily Crist in Florida. But those aren't true third party victories.
The next closest thing is when a candidate with a third party ideology, with backing from a third party voting bloc, runs as a dem or rep. The Pauls are the obvious example. And of course, those guys know better than to run as Libertarians.
- wolf