1. Perhaps, yes. The 2010 model differed greatly from the 2008 model, so it's not an unreasonable assumption that young voters might not show up in the numbers they did, but Republican turnout is as ginned up as it'll ever be and Romney still trails even in likely voter models.
2. This is a crappy assumption. The "undecideds" at that point usually break for the guy they think is gonna win since people like that want to vote for the winner. Romney has given them NO reason to vote for him, and that little video of him urinating all over the 47% isn't going to help matters.
3. It's been nine months of Romney shooting himself in the foot and making idiot statements over and over and over. If he was half-competent, I'd worry about this strategy, but with a month to go it's going to be difficult to start crafting a new narrative.
4. No they're not. The base alone doesn't win elections, and they're actively scaring away the people they need to help them. This person is under the impression that the base makes up 51% of the voting population. It does not.
5. No, it's not fatal, but I've seen no evidence that Romney has any ability to stop making idiot comments, and if we get into October and Romney still trails in the swing states you're going to have a hard time convincing me that Obama won't win.
I'm not overconfident, but I'm not ready to go Chicken Little either, and this guy is still whistling past the graveyard.