At this point, Romney essentially has the nomination wrapped up. Yes, people will point out that only a very small portion of delegates has been selected, but most of these contests are usually long over when the winner finally hits the mark that technically clinches it. Realistically, only some sort of external and utterly unexpected event could derail Romney now.
As far as I'm concerned, that's just about it. Newt will almost certainly stay in and fight through Super Tuesday in early March, although we don't know yet whether he'll continue going negative or not. And there's nothing wrong with that; to the extent that it was a real presidential campaign in the first place, there's no reason for him to drop out at this point. It's just that we, as observers, can tell that he continues to have no realistic chance of winning -- and if anyone doubted that, it's pretty obvious by now that he's just as vulnerable to attacks as anyone familiar with his record would have anticipated.
More comments on Florida and the GOP race tomorrow, most likely. For now, congratulations to Mitt Romney.