Political action committees report spending $36 million in Arizona on advertising independent of candidates, including $19 million in the state's U.S. Senate race.

The latest campaign finance reports show the committees, known as PACs, spending $11 million targeted to Republican Senate candidate Jeff Flake and $8.1 million targeted to his opponent, Democrat Richard Carmona. The figures include spending both in support of and opposition to the two candidates.

Such PAC spending is allowed without limits as long as the PACs don't coordinate with the candidates and their campaigns. That comes in the wake of the 2010 U.S. Supreme Court decision known as Citizens United vs. Federal Election Commission, in which the court said corporations and unions cannot be restricted in independent political spending.

The biggest amounts of independent spending by PACs in the Flake-Carmona race were $3.6 million in mostly television commercial purchases by the National Republican Senate Committee and $3.1 million in ad production work and TV ad purchases by the Democratic Senate Campaign Committee.

The National Republican Congressional Committee spent nearly $2.4 million on TV ads opposing Democrat Ann Kirkpatrick in her Congressional District 1 race against Republican Jonathan Paton. The committee also spent $753,000 on ads opposing CD 2 Democratic candidate Ron Barber.

The Democratic Congressional Campaign Committee spent $1.7 million on ads opposing Paton and $452,000 on ads opposing Republican Martha McSally in her CD 2 race against Barber.

With much of the campaign spending for advertising opposing candidates, some are saying the campaign has taken on an ominous tone that could be turning off voters. National Public Radio reported this week that negative ads are outnumbering positive 7-to-1 nationally.

“I don’t think there’s any question that the influx of money as a result of Citizens United has given both campaigns and all these super PACs the dollars necessary to buy many more television ads than we’ve ever seen before," the head of the National Institute for Civil Discourse told Arizona Week in an interview.

Carolyn J. Lukensmeyer, executive director of the institute based at the University of Arizona, said she was worried that all the negativity could cause voter turnout to decline.

Also on Arizona Week, UA political scientist and former Tucson mayor Thomas J. Volgy called the negative campaigning the worst he has seen.

“It’s never been this bad," Volgy said. "Four years ago, it had never been that bad. And, I think if this trend continues, we’re going to be sitting here four years from now saying, it’s never been this bad.”

Volgy said he is not certain it will affect voter turnout as much as others say.