U.S. Rep. Erik Paulsen hugged his wife, Kelly, during his concession speech last month. His decision to run negative ads damaged his Mr. Nice Guy brand. (The Minnesota Star Tribune)

It's easy to be cynical about politics and especially about negative ads.

Minnesotans were bombarded with tens of millions of dollars worth of political ads this year — the vast majority of them intoning in a dark, whispery voice how one candidate or another was so bad you wouldn't leave your kids alone with him.

Given all the money the campaigns spend on polling and focus groups and to produce the ads and purchase the TV time, a reasonable — and depressing — response during the campaign is that if they didn't work, they wouldn't use them.

But it's not always true. Negative ads can occasionally backfire, which may be what happened in the Third Congressional District race in which Democrat Dean Phillips beat U.S. Rep. Erik Paulsen, a Republican.

Zach Rodvold, Phillips' campaign manager, said they saw this in their own internal polling, which was conducted by Greenberg Quinlan Rosner, a widely respected Democratic firm.

A barrage of attacks accused Phillips of not giving his coffee shop employees health insurance when the shop first opened. (Phillips did offer insurance later.)

The ads were effective, insofar as people in the district became aware that Phillips was Paulsen's opponent and that he owned a coffee shop and didn't give his employees health insurance.

The problem with the attack was that the voters didn't expect a coffee shop owner to provide insurance.

The ads also helped raise Phillips' name identification in the district — one of the biggest challenges for any first time candidate — from 30 percent in April to 80 percent in August.

And the ads highlighted the health care issue, which was not a good one for Republicans this year. The protections offered by the Affordable Care Act have become increasingly popular in recent years, and Paulsen voted to repeal them.

Another set of ads tried to tie Phillips time as a volunteer on the board of Allina Health to a sexual harassment scandal at the company. But the factual claims were dubious at best, and Paulsen drew an unusually personal rebuke from some pillars of the community, including the business community. Bill and Penny George took to the pages of the Star Tribune Op-Ed page to call the ad "an outrageous lie" from a "former paragon of political civility."

Indeed, the ads damaged Paulsen's brand, which was Mr. Nice Guy. A Democrat told me once in 2016 that Paulsen was unbeatable because he looked like the husband or brother of everyone who lives in his congressional district.

It's easy to second-guess difficult tactical and strategic decisions. And Paulsen can hardly be blamed for fighting for his life in a very challenging political environment. If he had gone all positive, critics would be saying that he should have gone after Phillips.

But his defeat still offers an important lesson: Humans may be filled with bloodlust, but they'll throw you out if they catch you kicking a puppy without a good reason.

J. Patrick Coolican 651-925-5042 Twitter: @jpcoolican patrick.coolican@startribune.com