(FORTUNE Magazine) – The spring primaries are over, and the survivors are staggering amid the rubble. Though bowed and bloodied, they have learned some lessons: Don't carp about an economy that's roaring. Don't criticize incumbents at a time of tranquility. And for gosh sakes, be careful about those negative ads.

It may not exactly be morning in America, but it certainly isn't high noon either. Listen carefully to the backroom talk, and you'll conclude that politicians--God's geiger counters--are about to go negative on the negative ad. There's an easy explanation. In Pennsylvania's Lehigh Valley, on the plains of Nebraska, and in the cities and suburbs of California, big negative offensives were bigtime failures. In the 15 years since the National Conservative Political Action Committee took the negative national, the negative ad has had a simple, alluring image among political strategists: nuclear weapon. After this winter and spring of contentment, the negative ad has a new image: boomerang.

Financier and businessman Al Checchi, who served as his own collateral during his $30 million gubernatorial primary campaign in California, suffered the most collateral damage. The more he bombed away, the bigger bomb his own campaign became. His road to oblivion in the costliest statewide primary race ever was paved with the negative ad. He did, to be sure, destroy the candidacy of his big-spending rival, Rep. Jane Harman. But he destroyed himself as well, permitting the aptly named Gray Davis to streak to the gubernatorial nomination. Look deep in the California polling data, and you'll see an astonishing correlation: The more negative the campaign, the more negative the public's attitude about the candidate.

"The whole political dialogue has fouled the waters," says Paul Maslin, Davis' pollster. "People are fed up with negativism."

Checci wasn't the only one to learn that the hard way. Rep. Jon Christensen, the Omaha conservative and once the favorite in the gubernatorial race in Nebraska, didn't even make it to the general election. A religious conservative, he committed one deadly sin: He distributed a flier suggesting that one of his rivals, Mayor Mike Johanns of Lincoln, supported pornography on local cable. GOP Sen. Chuck Hagel was so outraged that he took the unusual step of criticizing a fellow Republican during a primary campaign. "Here was an effective congressman who didn't have to resort to this sort of nonsense," Hagel told me later. "Campaigns are not about telling people what's wrong with the other guy." Johanns finished first, Christensen third.

It's working the same way on the congressional level this spring. The Republicans held a classic shootout in eastern Pennsylvania in May. Bob Kilbanks, a real estate agent and social conservative, and Joseph Uliana, a state senator with establishment credentials, beat each other up so badly that Pat Toomey, an Allentown restaurateur whom the pros hadn't taken seriously, made off with the GOP nomination.

Politicians aren't hurtling toward unilateral disarmament, of course. Every political strategist knows that a crisply delivered jab can turn into a knockout punch. But you can expect far fewer negative ads this fall, and the ones you do see may be tamer than usual. The new mood fits in with the times. "Negative ads play against the fact that everyone wants to be at the beach anyway," says Stephen Hess, the veteran political analyst at the Brookings Institution. "The negative ad is like any fashion or fad. This, too, has passed." Let the word go forth: This is not the Year of the Pit Bull.

DAVID SHRIBMAN is the Washington bureau chief of the Boston Globe and a Pulitzer Prize-winning political reporter.