Under James Carville, Paul Begala & Co., Bill Clinton’s 1992 campaign team had a series of mantras:

Define your candidate before they do. While you’re at it, define their candidate, too. Let no allegation go unchallenged. If the other side needles you, slap them. If they slap you, punch them. If they punch you back, punch harder. If they use a knife, use a gun. And don’t wait to play defense: If you even think they are going to attack, attack them first. Come to think of it, don’t wait—just attack them anyway.

This kind of campaigning has its advantages, as none other than Bill Clinton and Barack Obama (and, yes, George W. Bush) can attest. But winning that way makes governing more difficult.

For starters, those on the losing end aren’t inclined to work in harmony with a president (or a political party) who won in this fashion. Such suspicion can be overcome, as Clinton showed on NAFTA, but only when oiled with the dual lubricants of bipartisanship and compromise—and that’s important: NAFTA was the signature domestic policy initiative of Bill Clinton’s first term. The Affordable Care Act was Obama’s.

That’s a big difference, but there’s an even more fundamental consequence of bare-knuckles campaigning: It’s addictive. Obama won the presidency in 2008 with an aspirational appeal. To retain the presidency, however, he and his lieutenants ran a low and mean-spirited campaign that sought to make Mitt Romney seem an unfit human being, while delegitimizing his political party.