The willingness of candidates to go negative tends to deter opposing candidates from spreading lies because they don’t want to risk getting blasted in return. In a 1996 article in Political Science Quarterly, William G. Mayer wrote that a ban on negative campaigning would allow candidates to begin every speech with the words, “I think I can say without fear of contradiction. …” and then lie their heads off.

Positive campaigning has its merits. Everybody wants to hear a candidate tell his story and present his vision in his own words. But endlessly positive campaigns are an informational dead end. When you buy anything—a dishwasher, a car, or a house—you want to know the upside and downside of your purchase. Just as a salesman will rarely point out the flaws in the object he’s selling, a candidate will almost never review the flaws in his candidacy. Only when campaigns go negative (or when the press goes digging) is the candidate revealed in full.

Non-aggression pacts like the one observed by the Sanders and Warren inevitably expire. According to a Monday report by CNN, Sanders and Warren formalized their treaty in a December 2018 meeting in which they vowed not to savage each other if they faced-off in the 2020 presidential campaign lest they wound the progressive movement. But such pacts always collapse as the voting starts, says Kerwin C. Swint, the author of Mudslingers: The Top 25 Negative Political Campaigns of All Time. “When to attack is always a matter of calculation,” says Swint, a professor at Kennesaw State University and former campaign consultant. “The vital calculation is ‘when does going on the attack benefit me and not one of the other candidates?’ ”

“Sanders is an aggressive candidate to start with, his syntax is rough and choppy, and he is very critical of things he doesn’t like,” Swint says. “He probably regrets being too nice to Hillary in 2016, particularly with the knowledge that Clinton and the DNC were gutting him in secret. He may be thinking to himself: ‘By God this is my last chance; I’m not going to play nice this time.’”

Continuing to treat the campaign as a tea party puts Sanders at a disadvantage. There’s not enough room for both Sanders and Warren in the primaries, Swint notes. “They appeal to too many of the same voters. The sooner he can get her out of the race, the better his chances become of making it a fight with Biden at the convention,” he says. Hence, Sanders’ strategic turn toward the negative.

Good for Bernie. There’s no way Sanders can distinguish his populist progressivism from Warren’s brand of professorial progressivism and peel off the votes he needs to win—which is the whole point of a campaign, right?—without convincing voters who lean toward her that she’s out of touch. If Sanders turns out to be right, he’s helping party members make an informed decision. If Warren fights back and disproves him, the voters come out on top again. If you’re a Democrat, this sort of campaigning ain’t negative. It’s positive.

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The craftiest form of negative campaigning is that which a candidate performs against himself. Called “inoculation” by Mayer, it occurs when a candidate preempts a negative attack by getting there before his opponent with a more anodyne version that disarms the ill information. Send inoculation via email to [email protected]. Also, see my 2015 piece on negative campaigning. My email alerts sealed a non-aggression pact with my Twitter feed. My RSS feed is neither positive nor negative. Just dead.