I know the President's taken a lot of flack already for not bringing up the 47%, but I'm going to pile on. There was an obvious place to use it.
"Governor, you have attacked 47% of Americans for not paying income taxes. (Although, of course, as you forgot to mention, they pay lots of other taxes.) The experts say your tax plan only pencils out if you're going to raise some taxes on the middle class. How can you expect anyone in that 47% to believe you when you say you won't raise their taxes?"
That said - remember, anyone can have a bad day.