Another trend from the Rasmussen national poll shows both the gap in enthusiasm and the lead Romney has with INDs contracting in Obama's favor. The whole "undecideds go for the challenger" argument is one of those things that makes sense, but there's little evidence of it occurring in reality. It happened for Reagan, but hasn't really occurred in a meaningful way since.
If the fence-sitters decide to stick with Obama and Romney's lead with INDs collapses then it requires - obviously - an even greater GOP turnout.
We'll know in three days!