Voters in a key part of swing state Pennsylvania have been subjected to a deluge of campaign ads ahead of Tuesday's vote, with candidates spending billions of dollars to boost their chances nationally.

Alongside roadside billboards, newspaper ads and targeted online campaigns, TV ads remain vitally important to candidate efforts to boost their profiles and attack their rivals.

During the 8:00 pm to 11:00 pm primetime slot on the last Wednesday before election day, viewers of the NBC affiliate serving Philadelphia and key surrounding swing counties were shown 22 political ads.

Of those, eight were explicitly pro-Harris or anti-Trump, six were anti-Harris and pro-Trump, while eight were for local races such as the Senate and attorney general, AFP analysis showed.

Under the US electoral college system, seven battleground states -- and sometimes individual counties within those states -- carry outsized influence over the overall result of the presidential election.

The ads, which sometimes run back-to-back and create the bizarre spectacle of an anti-Harris attack ad following a spot highlighting her achievements, ran throughout three dramas set in Chicago.

Former South Carolina journalist and blogger Brad Warthen said that he only encounters the TV political ads when watching live sports.

"I love the baseball, but could do without the ads. They're depressing," he said.

In the US, major TV networks including NBC, ABC, CBS and Fox cover the entire country, but are operated by local affiliates that sell their own ad space, meaning campaigns can target specific regions and demographics.

Industry monitor Emarketer estimates that by the end of the 2024 election, $12.32 billion will have been spent on political ads, up from $9.57 billion total political ad spending in 2020.

Broadcast TV is a popular choice for political campaigns as it has more available minutes than streaming services.

This year, $7.06 billion of that expenditure will go on television ads -- a 7.5 percent increase on 2020.

"I recently started screaming at the TV to stop playing the same political ads over and over," wrote author Aimee Davis online.

Culture war issues

Presidential races provide a massive cash injection for traditional TV broadcasters, with BIA Advisory Services forecasting that political ads will account for nearly seven cents of every dollar spent on local advertising.

"This political spending estimate represents a significant increase of 21.3 percent over the last general election that took place in 2020," BIA said in a market update.

In the primetime slot on the NBC10 WCAU channel, viewers were shown a cinematic clip painting a dire picture of the economy, global conflict, crime and political violence before showing a stoic-faced Donald Trump walking towards the camera.

Moments later, after a clutch of bubbly ads for Apple products and Thanksgiving sales, a pro-Harris spot showed a helmeted Pennsylvania steelworker proclaim "Elon Musk is voting for his money, I'm voting for mine."

Trump has campaigned with billionaire Musk in Pennsylvania and the tech tycoon has poured money into efforts to get Trump elected in the state, which was a thriving center of steelmaking until widespread deindustrialization left many factories empty and communities in decay.

A pro-Democratic ad featuring female medical professionals attacked David McCormick, the Republican candidate for the Senate, control of which could be decided by Pennsylvania voters, for his anti-abortion stance.

A Republican ad then attacked his rival, sitting Democratic Senator Bob Casey over the spread of fentanyl in the state, while another slammed Casey as being "too liberal for Pennsylvania."

The ad highlighted his support for transgender rights, showing an athlete competing in women's athletics who the voiceover then mis-gendered.

Anti-abortion and anti-transgender rights ads have been aired by candidates in many markets, highlighting the divisive "culture war" issues framing the election, drawing condemnation from commentators.

"It is dehumanizing, it takes an issue... and it treats it like it's some outrageous position to take," said Parker Molloy, an author and blogger who has written on transgender issues.

One graphic pro-life campaign ad prompted local channels including Kansas City-based FOX4 to explain that "according to the Federal Communications Commission rules... it is illegal to block or modify these ads in accordance with federal law."

© Agence France-Presse New York, United States. By Gregory WALTON