Headlines about Lori Swanson's work as attorney general flash across the TV screen. Erin Murphy speaks to the camera while marching down the street, followed by a crowd of supporters. Tim Walz talks to students in classrooms and school hallways. Tim Pawlenty and Jeff Johnson volley attacks at each other's records.

Minnesota's airwaves are filled with 30-second snippets of what candidates would — or would not — do if they land in the governor's office. And it's not just the five major gubernatorial hopefuls competing for airtime ahead of the upcoming primary election. Congressional candidates are also paying tens of thousands of dollars to get their message out to viewers.

And it's only August. If the lakes, trails or patios aren't beckoning, then air conditioning and Netflix probably are. As more people opt for streaming services over cable or broadcast TV and Minnesotans soak in the short season of sun, the question emerges: How effective are the expensive ads?

"Everyone's kind of checked out that's not really a hard-core insider at this point," said Minnesota Republican Party Chairwoman Jennifer Carnahan, who previously worked in corporate marketing. "So then you also have to question what impact is everything having right now outside that core base of reliable voters on both the Republican and DFL sides. Are people even paying attention? And I don't think they are."

Still, millions in campaign funds are going to ads. Candidates for governor have spent $688,632 to air 930 commercials on WCCO-TV alone, contract agreements filed with the Federal Communications Commission show. Those messages crop up throughout the day.

Morning viewers of "The Price is Right" have likely heard the dramatic music and a man's voice proclaiming that Swanson and running mate U.S. Rep. Rick Nolan are "Minnesota's tested, proven, progressive team." People tuned in to "The Late Late Show" may catch Walz talking about his time as a high school teacher and his plans for affordable prekindergarten and expanded technical education. "CBS This Morning" fans have undoubtedly heard Murphy say, "I'm running for governor because we've got big fights ahead, like health care for everybody and stopping the NRA."

The number of contested primaries this year has made for an unusually packed summer season of political ads and driven up the cost to air the commercials. Candidates are fighting to differentiate themselves from their opponents, and broadcast television — albeit the most costly way for campaigns to reach voters — still allows politicians to tell their stories to a wide audience.

For Johnson, who was the last candidate in the governor's race to put out a TV ad, that meant striking a contrast with fellow Republican and former Gov. Pawlenty.

"Tim had his chance and he blew it. I'll actually shrink the budget, dismantle the Met Council and rein in arrogant state agencies," says Johnson, standing in front of a cornfield in a plaid shirt and jeans.

Pawlenty has launched two ads so far. In his initial ad, he takes aim at Johnson, saying he proposed a property tax increase as a Hennepin County commissioner and is a "tax-and-spend career politician." Johnson disputed the claims, defending his proposed tax levy increase as lower than what his colleagues wanted and pointing to his high rating from the Minnesota Taxpayers' League. Pawlenty's second video, released Thursday, focuses on stopping benefits for immigrants living in the country illegally.

Negative ads are more effective than issue-based ones, as they tend to resonate emotionally with viewers, University of Minnesota political science professor Andrew Karch said. But in general, he was doubtful that TV ads will have much of an impact on mobilizing voters and encouraging people to vote in August.

Campaigns have slowly been shifting resources to more targeted social media ads, Karch said, which can be more cost-effective.

There is also an evolution to more targeted TV ads, state DFL Chairman Ken Martin said. Addressable ads became more widely used in the 2016 election, he said. They allow a candidate or company to show an ad only to certain targeted households watching a given program.

"When you buy a TV commercial on [W]CCO, for instance, you're hitting a lot of eyeballs of people you don't really need to communicate with," Martin said, while addressable ads are precise.

The governor's job, U.S. Senate and House seats, attorney general, Minnesota House and other political positions are all on the November ballot. That has driven up not only the price of broadcast and cable TV ads, but of radio advertisements, digital ads and mailers, Martin said.

"All those costs have gone up because there's just a lot more people buying it. And it's supply and demand, all of it," he said. "The cost to run a campaign is exceptionally higher than it was in 2016 because of all the candidates on the ballot."

In a typical general election it would cost between $800,000 and $850,000 to saturate the metro area market with a broadcast TV ad, Martin said. Now, he said, the price of airing a commercial enough times to make people remember it is closer to $1.2 million, which he called "egregious."

But television ads do help primary voters learn about the candidates, even if it's just recognizing their names and what they look like, UCLA political science Professor Lynn Vavreck said in an e-mail. And candidates don't want to let opponents out-advertise them, she said.

However, Vavreck said the effects of TV ads "are small and they go away quite rapidly — most of the impact is gone within a few days of the ad being aired."

While the impact of a single commercial may be short-lived, Carnahan and others said ads could have a cumulative effect on voters, causing them to tune out this fall. In some election years people are not inundated with ads until September, she said.

"We've been seeing TV ads in Minnesota since, what, June? So that's a solid 3½ months sooner than when we normally start to see them," Carnahan said. "And so you wonder, is there going to be a point of diminishing returns?"

That puts pressure on candidates and outside political groups — which are also adding to the cluttered airwaves — to tell a compelling story, said Joe Davis, executive director of the progressive Alliance for a Better Minnesota. The group has aired two commercials featuring women talking negatively about Pawlenty's time as governor.

"The more and more of them that are run, it's definitely a concern," Davis said. "A stereotypical political ad, once we've started running these forever, is probably going to get tuned out."

Jessie Van Berkel • 651-925-5044