For while there, conservatives saw the hand of George Soros behind every conspiracy. It was always a little strange, not because there wasn't a certain truth underneath it—Soros has, in fact, given lots of money to liberal political causes (and he is an actual international Jewish financier, which certainly set a certain type of mind buzzing)—but because the idea of a billionaire using his money to shape America's politics isn't something conservatives object to. Quite the contrary; they think there ought to be a lot more of it.
Democrats, on the other hand, are not so friendly to the idea, which is why it's understandable that Charles and David Koch have taken on a larger role in the liberal imagination than Soros had in the conservative one (they've also spent a lot more money on politics than Soros ever did). But can Democrats convince voters who are not already liberals to be mad at the Kochs? That's how they're responding to the brothers' involvement in multiple Senate races this year, fighting back against the Koch's ads with with a public campaign against them.
While I don't think it's impossible that this could work, I'm skeptical. Greg Sargent explains the thinking:
Dems hope to focus voters on [Republicans'] actual positions by painting candidates as beholden to an agenda held by outside interests. The Koch brothers are a proxy for special interests in general, an easy-to-understand concept designed to create a narrative framework within which voters might reach the general conclusion that GOP candidates' priorities aren’t in their states’ interests; they are serving something—or someone—else.
This is similar to the Dems' Bain strategy of 2012. This was widely seen as nothing more than an effort to paint Romney as a heartless plutocrat. In reality, the goal was to create a framework within which voters could be persuaded of his actual policies and priorities, which research had shown voters simply weren’t prepared to accept.
Fair enough, but I don't really think you can separate the the policy argument from the personal argument, so long as the Democratic policy argument is that Republicans want to help rich people while Democrats want to help regular folk. The argument about Romney was always twinned: He wants to screw the little guy, Democrats said. And who'd do something like that? A guy like Mitt Romney, that's who.
It does seem kind of irresistible to embody that argument in two brothers who, if you put them together, would tie Bill Gates as the richest American with an astounding $72 billion fortune, and who have devoted much of their time to ensuring that the political system is as solicitous as possible toward fabulously rich guys like themselves who want to keep wages low for workers and taxes low for the wealthy, and would prefer not to be bothered by inconvenient environmental rules. The problem is that most Americans have no idea who Charles and David Koch are. Yet they're already being featured in ads like this one in which we see their picture without any explanation. I'd be interested to see a poll on their name ID, but until somebody does one, I'd guess that maybe 10 percent of voters are familiar with them. Now maybe between now and November, Democrats can successfully educate enough of the voters on the Kochs to have a real impact. But it won't be easy.