Column: Best and worst ads in this year’s U.S. Senate races

It’s autumn in an even-numbered year, time for the hard-fought playoffs in our national sport. I am speaking, of course, about congressional elections.

If you live in one of the 11 states with a close race for the U.S. Senate, you already know this. Your television screen has been flooded with political advertising for months.

And it’s nasty this year — even nastier than usual. The nonpartisan Wesleyan Media Project analyzed thousands of Senate commercials across the country last month and found that 74% included negative information about one of the candidates, a higher number than the same research group found in either 2010 or 2012.

In one contest — Louisiana’s race between Sen. Mary Landrieu (D-La.) and Republican Bill Cassidy — the percentage of positive ads in early September came to … exactly zero.

“Voters are seeing an attack on a candidate … in 3 of every 4 Senate ads,” Michael Franz, the project’s co-director, wrote in a blog post.

Here are my picks for some of the best and worst ads of the year so far, all of them watchable on the Internet regardless of where you live:

Worst Democratic attack ad: Sen. Mark Begich (D-Alaska). In August, Begich ran a spot accusing his GOP opponent, former Alaska Atty. Gen. Dan Sullivan, of approving light sentences for sex offenders — including one who, after his release from prison, was accused of murdering a couple and raping their 2-year-old granddaughter. Two problems: there was no evidence that Sullivan handled the earlier case, and the victims’ family, offended by the ad, demanded that Begich take it off the air. He did.

Worst Republican attack ad: David Perdue, a Senate candidate from Georgia. Perdue has a spot up charging that his Democratic opponent Michelle Nunn “funded organizations linked to terrorists” when she ran the Points of Light Foundation, which was founded by former President George H.W. Bush. But the charge turned out to be a mirage: Points of Light allowed individual donors (not Nunn) to direct gifts to Islamic Relief USA, a Muslim organization that the U.S. government does not consider linked to terrorists.

Most frequent appearance in campaign ads for candidates he doesn’t support: President Obama. Not surprisingly, Republicans across the country are trying to cast the race as a referendum on an unpopular president. And Obama has certainly given them fodder. Just last week, he said: “I’m not on the ballot this fall … but make no mistake: these policies are on the ballot.” Republican candidates have already made ads featuring the president’s statement, which former Obama advisor David Axelrod characterized as “a mistake.”

Most creative use of animals: A tie between Louisiana Republican candidate Rob Maness and Iowa Republican candidate Joni Ernst. Plenty of candidates get photographed feeding horses or playing with dogs. But this year, a Maness commercial shows him subduing an alligator — a real one. The Ernst commercial shows her in a barn, surrounded by pigs, bragging: “I grew up castrating hogs on an Iowa farm … Washington’s full of big spenders. Let’s make ‘em squeal.” She does not, for the record, demonstrate her technique.

Best positive ad: Sen. Mitch McConnell (R-Ky.). The Senate Republican leader has faced an unexpectedly tough challenge from Democrat Alison Lundergan Grimes, and there’s been plenty of negative advertising on both sides. But McConnell’s most memorable ad is one that goes against the grain: It features Noelle Hunter, a Kentucky mother whose ex-husband kidnapped her 4-year-old daughter in a custody dispute. “Mitch never stopped fighting for us,” Hunter says, tearing up. “I can’t even talk about him without getting emotional. He cares.”

There’s no mystery why campaigns resort to negative advertising: It works. Decades of research has shown that voters remember attacks more often, and more vividly, than any of the positive information a candidate delivers about his own positions.

The Wesleyan Media Project found that this year’s Democratic Senate campaigns were more negative, on average, than GOP campaigns. Meanwhile, Republican campaigns relied more on “contrast” advertising, in which the candidate’s positive record is held out in contrast to the opponent’s record.

The different approaches reflect the nature of this year’s tight Senate races: a long list of Democratic incumbents fighting off Republican challengers. Negative advertising is most powerful when it’s directed against a candidate voters don’t know well. And some scholars, such as John G. Geer of Vanderbilt University, argue that negative ads aren’t necessarily a bad thing. “Negative ads can be good because they generate a conversation,” Geer told me.

The key, of course, is knowing whether the conversation is truthful or not. That’s why the most important new factor in campaigns is the rise of fact-checking organizations such as FactCheck.org at the University of Pennsylvania’s Annenberg Public Policy Center. And that’s why, oddly enough, the most encouraging event in the campaign year may have been the furor kicked up by Mark Begich’s nasty ad in Alaska and David Perdue’s ugly innuendo in Georgia. Deceptive advertising only works if the perpetrators are allowed to get away unscathed — or, worse, rewarded by the same voters who insist they hate negative ads.

doyle.mcmanus@latimes.com

Twitter: @doylemcmanus