Twelve years ago, in early August, an obscure political group called Swift Boat Veterans for Truth rolled out an ad in three hotly contested battleground states. It featured several veterans who served in John Kerry’s unit in the Vietnam War alleging that the Massachusetts senator had falsified his war record, a central pillar of the heroic life story he had been telling for months on the presidential campaign trail. The media put the ad’s claims in the spotlight for much of the slow news month of August, and even though they were widely denounced, Kerry became damaged goods only a month after accepting the Democratic nomination.

Meanwhile, the candidate who benefited from the “swiftboating,” President George W. Bush, suffered no real blowback from ads that smeared a decorated war veteran on his behalf. Voters—other than angry Kerry supporters—didn’t hold Bush responsible for the sketchy commercial that did so much to ensure his reelection.

This year, in her coming face-off with Donald Trump, Hillary Clinton needs to do what George W. Bush did back then: Find a way to take the opponent down, hard, but without voters connecting her to the attacks. Bush was unpopular in 2004, and couldn’t risk muddying himself any more. Clinton is now even less in favor with the American public: She has the second-lowest favorability ratings of any (presumptive) presidential nominee in the history of polling. Fortunately, Trump ranks Number One on that list. But even so, Clinton needs to steer clear of looking like a mudslinger.