Hillary Clinton is running this ad in Pennsylvania, where the primary is one week from today. It is arguably her toughest ad against Barack Obama yet, one which could have been put together by the McCain campaign.

It attacks his clumsy choice of one word — the now-infamous “bitter” — which he has conceded was a poor choice, while not backing away from the message he sought to convey. Do notice the subtle use of people who comprise much of her base, those who would never be mistaken for upscale Main Liners, particularly the woman, part of a couple, who refers to “people like us.”

One interesting thing about this ad is that Clinton has adopted an effective, attention-getting Obama technique I noticed in his ads for the Vermont primary: having the “I approved this” line at the open.