When Rep. Steve Israel (D-N.Y.) has trouble sleeping, it's because of the Koch brothers.

"On the issue of the Republican super PACs and the Koch brothers, honestly, it is the one thing that makes me toss and turn," Israel, the head of the Democratic Congressional Campaign Committee, told reporters Wednesday.

And why wouldn't he? Americans For Prosperity, a group backed by the billionaire industrialist brothers, has been the dominant third-party group spending money on House and Senate races so far this cycle. Through late March, AFP had run more than double the ads of its closest Democratic competitor -- House Majority PAC -- in nine key House races.

Democrats realize they can't compete with AFP, dollar for dollar. So they have been pushing back by trying to villainize them and make them into electoral bogeymen. Senate Majority Leader Harry Reid (D-Nev.) routinely mentions them in a negative light; he did it again Tuesday. Democratic congressional campaigns do, too. Perhaps most notably, Democratic-aligned groups are launching paid advertisements with increased frequency that seek to inject the Koch brothers into the campaign debate.

"I think the Koch brothers are beginning to overextend. They are becoming a brand," Israel said. He pointed to two battleground districts where AFP has been on the air and House Majority PAC has pushed back: Arizona's 2nd district, represented by Rep. Ron Barber (D); and West Virginia's 3rd district, represented by Rep. Nick Rahall (D). The Democratic super PAC targeted the Koch brothers and Barber's opponent Martha McSally (R) directly in a January ad. In a more recent ad in West Virginia meant to defend Rahall, the group is less direct, mentioning "New York billionaires." In the battle for the Senate, the effort to turn the Koch brothers into the bad guys has been more robust. Democratic Sen. Mark Begich's first ad in Alaska pushed back against the Koch brothers. Senate Majority PAC has followed suit in other races, targeting Republicans running in North CarolinaLouisiana and Michigan. AFP has spent some $30 million on Senate races and key House races already.

But here's the really big challenge for Democrats: Most of the public doesn't know who the Koch brothers are. A recent poll showed that 52 percent of Americans said they didn't know about Charles and David Koch. Another 11 percent had no opinion. Democrats have seven months to change those numbers. They're hopeful that if they can raise the public profile of the Koch brothers, it will help them in the midterms. Why? Because polling also shows that among those who have heard of the brothers, opinions were predominantly unfavorable. Democrats also feel that mentioning the Koch brothers frequently is a way to gin up Democratic base enthusiasm and spur donors to give more to them.

Whether or not it works is what remains to be seen. Democrats tried and failed in 2010 to make campaign finance issues matter at the ballot box. Voters don't tend to be persuaded by process arguments, so Democrats must be effective at winning over voters on policies favored by AFP and the Kochs.

They are starting to put more and more money behind the effort. We'll find out in the months ahead whether Israel starts sleeping better -- or not.