With that criteria I would say that Santorum is not yet a serious candidate. He doesn’t have the funds raised or the organization in place to run in all the States needed on Super Tuesday.
And everyday the road gets longer and harder without the funds in hand and the people in place.
South Carolina is a make or break election. If Romney (or Paul) wins, the game is over. Money dries up from the other candidates and it’s trying to put lipstick on our pig to beat the lipsticked pig the Democrats are stuck with.
If someone else wins, all the money from the “Not-Mitt” movement shifts to them. Then we have a race to the nomination. If Santorum wins South Carolina, he will become a serious candidate, but he just isn’t one yet.
Fine. So he’s a potentially serious candidate. The way I see things, this is the same as being a serious candidate.