WASHINGTON — One ad depicts Colorado Democratic Senator Mark Udall as a truth-twisting clone of President Obama. Another portrays North Carolina Republican Senate candidate Thom Tillis as a tool of special interests who destroys families.
These televised attacks reveal two intersecting themes of the 2014 races: in one of the most negative midterm elections, an unprecedented amount of funding comes from secret donors.
While vitriolic ads are hardly new, voters this year have witnessed an indundation. Nearly three quarters of Senate ads in a two-week period between August and September showed a candidate in a negative light. This outpaced the last two cycles at that time, according to Wesleyan Media Project, a nonpartisan group that researches advertising in elections.
The rise in undisclosed donations stems from the Supreme Court's Citizens United decision in 2010, which allows outside groups to spend unlimited amounts of money as long as they don't coordinate efforts with a candidate. This marks the first midterm in which such practices are in full force.
The impact is visible online and on television. One of every 16 television ads in US Senate races from January 2013 through August were paid for by a single group, Americans for Prosperity, according to the nonpartisan investigative Center for Public Integrity and advertising tracking service Kantar Media. AFP serves as a nonprofit advocacy arm of the political network backed by conservative billionaire brothers Charles and David Koch.
"The increased presence of outside spending is one of the reasons why the elections in the last two cycles have been so negative," said Michael Franz, co-director of the Wesleyan project. "Outside groups don't do positive advertising."
Election money draws from numerous sources, including a party's national organization, political action committees run by groups like labor and business, individual contributions and campaigns themselves.
The Supreme Court decision paved the way for Super PACs, which do not face restrictions on spending but do have to disclose donors. It also helped fuel the growth of political nonprofits, sometimes referred to as dark money, that do not need to make donors public.
These secret donor groups have attracted mega-contributors -- and criticism that a handful of the wealthiest Americans hold outsized influence on politics.
The Center for Responsive Politics, a research group that tracks money in politics, calculates dark money has hit a record for this point in a congressional cycle -- upwards of $100 million, and could at least double by Election Day. Undisclosed donor groups represent 23 percent of outside spending.
Republicans dominate this realm. A recent study by New York University's Brennan Center for Justice examined the most competitive Senate races and found 80 percent of pro-Republican independent spending came from dark money.
AFP has stated plans to spend at least $125 million on the elections. It and five other Koch nonprofits aired nearly 44,000 television aids from the start of the cycle through August, according to the Center for Public Integrity.
A recent digital AFP ad attacks Alaska Democratic Senator Mark Begich for his Obamacare vote, declaring in bold, red letters that he uttered "the lie of the year" by telling Alaskan families they could keep their insurance plans.
An AFP spokesman said such ads reflect the societal mood.
"There is a lot of genuine dissatisfaction already," said Levi Russell, an Americans for Prosperity spokesman. "What we want to do is make a connection with the policies that are causing that."
Crossroads Grassroots Policy Strategies, a political nonprofit co-founded by Republican Karl Rove, also is playing a sizable role. The group is running an ad that shows Arkansas Democratic Senator Mark Pryor distracted by phone calls as it blasts him for sacrificing independence and integrity. "Time to retire Mark Pryor" a narrator says.
The group, whose spokesman has said it raised $75 million, also created the anti-Udall ad.
Pro-Democrat political nonprofits are trying to catch up. Liberal groups make up 20 percent of undisclosed donor cash, and are taking aim at the Koch brothers.
Patriot Majority USA, run by a former aide to Senate Majority Leader Harry Reid, has spent more than $7 million on political ads, including the one attacking Tillis.
The League of Conservation Voters, a political nonprofit that often supports Democratic candidates, plans to spend $25 million this election. The environmental group has dished out about $7 million on ads so far this year, with a small amount from a separate fund that discloses donors.
A recent ad flashes images of angry faces and accuses Iowa Republican Senate candidate Joni Ernst of decisions that would risk the health of families.
"These ads hold candidates accountable," said Jeff Gohringer, a league spokesman. "They work."
Political nonprofits have funneled even more money into the election than it appears. Many also created issue ads that don't promote a specific candidate. These only require disclosure 30 days before a primary or 60 days before a general election.
"The outside money is the money fueling these ads," said Kathy Kiely, managing editor for the Sunlight Foundation, a nonpartisan organization that pushes for open government."What these so-called independent groups are doing is allowing candidates to keep their fingers off the negativity."
Nonprofits aren't the only ones pouring money into the campaign or drumming up negativity. Candidates and their party committees also are responsible. Republicans have tried to tie Democrats to Obama, while Democrats have avoided campaigning with the president or mentioning him on the trail.
But many political nonprofits, through their special brand of funding, have dramatically increased the reach of attack ads.
"What is different is the volume," said Mattis Goldman, a Democratic ad consultant who has assisted with gubernatorial, Senate and mayoral races nationwide. "It feels more negative when it's really louder."