Clinton should know: She ran plenty of them against Barack Obama in 2008, and if this year's race stays close, you can bet she’ll run them against Sanders as well, before long. In fact, several of Clinton’s ads in 2008 made even more direct attacks on Obama, putting to rest the specious claim that Sanders is running the most-negative campaign in history. (Benenson should know, too: He was Obama’s pollster eight years ago, and that campaign ran plenty of negative ads against Clinton.) To take one example, in April of 2008, Clinton ran an ad in Pennsylvania seizing on Obama's comments at a private fundraiser that people in small towns “cling to guns or religion” to explain their frustration. The ad featured video of voters calling Obama “insulting” and “out of touch” with voters. (While many Clinton ads from 2008 have been taken off YouTube, you can find a good repository at Stanford University’s Political Communication Lab.)

The real story here is that the Clinton campaign is pursuing the same strategy she tried to use, without success, against Obama. Sanders is running on a more economically populist version of the “new politics” campaign that Obama ran in 2008, and Clinton is looking for any morsel of hypocrisy in an effort to dent his image and cast him as the kind of traditional politician from whom voters are recoiling. By seizing on any hint of negativity, she’s also trying to force Sanders into a box of his own making, keeping him from drawing the kinds of direct contrasts he may need to make in order to win. Never mind for the moment the many studies showing that negative advertising is actually quite effective, and whether voters actually care about the “negativity debate” is another question.

It’s a tricky game for both candidates. Sanders says he won’t run “negative ads,” but he will draw “a contrast” with Clinton on the issues. That can be a very blurry line, and politicians often use the word “contrast” as a euphemism to describe ads that are, in truth, quite nasty. “Let me tell you, I run vigorous campaigns,” Sanders said at that same opening press conference. Sanders is benefitting from the fact that nothing he’s said about Clinton compares to the mud-slinging going on in the Republican primary. And so far, Sanders is the one looking artful while Clinton risks coming off as desperate. But that can change as fast as the votes are counted in Iowa.

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