As for NV’s bellwether status, it has indeed voted for the winner in 24 of the 25 presidential elections from 1912 to 2008 (all but 1976). However, MO voted for the winner in 25 of the 26 presidential elections from 1904 to 2004, and the fact that it vited for McCain in 2008 wasn’t enough to deliver the presidency to him. And DE was the only state to go 12 for 12 from 1952 to 1996, yet it was unable to deliver the presidency either to Gore or Kerry. In other words, electoral bellwethers lead the way until they stop doing so.
The state that I think is likeliest to decide the 2012 elections, being close to a must-win for both parties, is OH. If OH does end up being decisive, it will be the 13th straight election in which it votes for the winner (and if Romney wins without carrying NV, no other state will have a streak longer than 5 elections).
Yes, Ohio has an excellent record as a bellwether. Not to mention it’s much larger than Nevada or Delaware. Missouri is now more Republican that average and Delaware much more democrat (and I fear Nevada is now becoming a little more democrat). Ohio remains a closely divided state. McCain did 1.2% better than his national showing.
Not counting Kennedy the last time it was wrong was 1944 (which was not that close of an election) when it narrowly voted for Dewey, before that 1892. No Republican has won without it (not counting 1916 when Wilson should have lost but easily won Ohio).
It’s unlikely Romney wins without it, not likely Obama does either.