I would take it as Christie meant—Romney was going to the definite chosen one—that is what would be going down as “a fact”. As in, when “it goes down in history” scenario; but with a tougher delivery with the added “sweetheart”—a little tough guy “James Cagneyish” delivered humor...when you say it like it is, end of story. Capisci?
I think Christie may have meant something entirely different. I do agree he was trying to come off as a tough guy. But you don’t say going down to a female and call her sweetheart and mean going down as a fact.
Just my two cents.