Senate Majority Leader Harry M. Reid has repeatedly questioned the Koch brothers' patriotism.

From the Senate floor to television advertisements across the country, Democrats are assailing Republicans for their alliance with billionaire industrialists Charles and David Koch.

Senate Majority Leader Harry M. Reid has repeatedly questioned the brothers' patriotism, accusing the GOP of suffering from an "addiction to Koch." A recent ad in Michigan, as in other places, features images of the Kochs with a grave warning that a GOP candidate seeks to aid the "wealthy and powerful."

The coordinated strategy is designed to try and counteract the tens of millions of dollars in attack ads funded largely by the Kochs and their network of conservative groups that have been pummeling vulnerable Democrats over their support for Obamacare.

Democrats are facing increasingly steep odds in the midterms, due at least in part to the apparent success thus far by conservative groups in targeting key races with hard-hitting ads.

Yet the Democrats' anti-Koch strategy is risky.

The brothers are not a familiar presence to many voters, making it hard to demonize them. Moreover, as Democrats have embraced the new era of big-money donations and super PACs in the wake of the Supreme Court's ruling in Citizens United v. Federal Election Commission, they, too, are growing more reliant on ideological billionaires such as Tom Steyer, the hedge-fund executive who plans to target Republicans over climate change.

While many Democratic operatives say they think the anti-Koch attacks will help mobilize the liberal base, several also said that Democrats must tread carefully.

"If voters see it as an overwhelmingly negative campaign, it'll effectively turn people off and keep them from voting," said Jerry Rephan, a Democratic Party county chairman in Arkansas.

Republicans point to their own past miscalculations to argue that the Democrats' Koch-centered strategy is little more than folly. The GOP's attempts in 2006 to decry Democrats for their reliance on billionaire George Soros proved ineffective, Republicans now say -- the Democrats won control of the Senate that year, giving them control of both chambers.

The focus on the Kochs comes as Americans for Prosperity, the political organization they finance, plans to target incumbent Democrats considered particularly vulnerable. The group has already spent more than $30 million as part of the Republican push to reclaim the Senate.

In television ads, radio spots, direct mail and e-mail releases, AFP has aggressively worked to tie vulnerable Democrats to the Affordable Care Act, which remains deeply unpopular in many of the states hosting tightly contested races this year.

AFP begins airing a new ad in Colorado today targeting Sen. Mark Udall for his support of the health-care law.

Democrats, in turn, have unveiled ads and mailers slamming the Koch-backed GOP candidates and the Kochs themselves.

Reid, for his part, has taken the unusual step of leading the attacks with sharply worded Senate floor speeches.

Among Reid's remarks: The Kochs are "un-American" and participate in a "subversion of democracy."

The intense spotlight has prompted the Kochs, who have long steered clear of the public arena, to lob sharp retorts back at the top Senate Democrat. That decision was driven in part by the personal tenor of Reid's attacks, which have been growing more intense over several years, according to a Koch spokesman.

"It is a time-worn tactic, but it's nothing more than that," said Robert Tappan, a spokesman for Koch Industries. "Right now, Sen. Reid is running scared."

Several prominent Republicans have rushed to the Kochs' defense. New Jersey Gov. Chris Christie declared the brothers "great Americans" during his address to the Conservative Political Action Conference earlier this month. Texas Sen. Ted Cruz said last week that it is "misguided" for Reid to "vilify private citizens."

Senate Minority Leader Mitch McConnell (R-Ky.) has argued that Democrats are hypocrites for attacking the Kochs while benefiting from their own wealthy allies, invoking Steyer's name during a Senate floor exchange with Reid earlier this month.

Steyer, of San Francisco, is seeking to build a network on the left to rival the Kochs that would spend as much as $100 million this year attacking candidates deemed unfriendly to the environment.

"It strikes me as curious that if we are going to demonize people for exercising their constitutional rights to go out and speak and participate in the political process, we would just pick out the people that are opposed to us and leave out the people who are in favor of us," McConnell said.

A spokesman for Steyer, Chris Lehane, described the GOP attacks as "real validation ... to what Tom is seeking to do. The attention only reinforces and elevates how the focus on climate as a wedge issue to be deployed to win elections is causing real concern on the Republican side."

The Democrats' strategy hinges on linking Republicans to policy positions they have that could benefit the economic interests of the Kochs, whose broad business interests include energy, agriculture and electronic components.

In Alaska, Democratic operatives have seized on the fact that the Kochs -- who are spending in an effort to oust Sen. Mark Begich -- closed a refinery near Fairbanks.

In Arkansas, those campaigning on behalf of Democratic incumbent Sen. Mark Pryor allege that his GOP opponent Tom Cotton only opposed the farm bill because that is the position of the AFP.

"It's not even about Tom Cotton and Sen. Pryor. This campaign by the Kochs is about them pushing their own interests," said Tyler Clark, chairman of the Washington County Democratic Committee in Arkansas.

Whether the voters will agree, or even care, is an open question.

The Kochs, for all of the attention they get from Washington politicians, remain relatively unknown to huge swaths of the electorate, according to the few polls that exist about their name recognition.

A poll of registered voters conducted in January for the Democratic-aligned America Votes found that Kochs had relatively low name identification in five battleground states, ranging from 29 percent to 37 percent, according to a person familiar with the results. The exception was Wisconsin, where AFP helped Gov. Scott Walker fight off a recall effort. There, 50 percent of people recognized the brothers.

Democratic operatives insist the strategy is more complex than simply using the Kochs for scare factor -- the larger goal is to link the Republicans accepting money from AFP to big business "outsiders."

"Voters understand that all of this outside money is coming from people who have agendas, even if they don't recognized their names," said Democratic strategist Bill Carrick.​