Ah, yes, viability is the key, isn't it?
You could say all of them need to "be viable", even the front-runners.
For instance; Rudy is the current front-runner, but since he cannot win the general, he is still not "viable" in any real sense of the word.
I won’t be voting for Rudy. While I appreciate his service associated with 09/11, we do not need any more RINOS. Hopefully NEVER AGAIN.