Obama's riff on "you didn't build that" remains, in my view, the most serious mistake of his campaign so far. There's a reason the Romneyites have seized on it and will use it – dishonestly, of course – again and again. It works. Here's a post from Steve Lombardo that tracks Romney's slow but steady rise in the polls – and sees Obama's gaffe as the turning point in the campaign before the conventions:

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Now there's a lot of noise in all that. But you can see Romney struggling before that dread quote, and gaining thereafter. It may end up a blip. But it still stings. Mr President, please don't listen to pious Massachusetts liberals as a guide to your election rhetoric. Warren will probably lose in Massachusetts she is so gratingly smug. You don't need to go down with her.