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Routine fundraisers don't usually trigger attack ads and headlines, but when the man raising a boatload of cash is billionaire conservative David Koch, the spotlight shines brighter.

That was the case on Sunday as Mitt Romney trotted around the Hamptons raising millions of dollars, stopping at Koch's shorefront estate for a party that cost $50,000 per person (or a deal: $75,000 for a couple).

The event, of course, was closed to reporters, so few people know what Romney or Koch said. Democrats have already made an ad charging that if Romney becomes president, he would give oil men like David Koch and brother Charles tax cuts and subsidies. Liberal protesters gathered at Koch's home to deride the affair.

The left has long hated the Koch brothers, Kansas billionaires whose outside-spending group Americans for Prosperity is tied to the tea party and has tried to tear down Democratic candidates through advertising. The group is a 501(c)4, which means it doesn't have to reveal from whom it gets money. David and Charles are said to be worth about $25 billion each, and according to reports, have said they plan to spend more than $200 million in the 2012 election cycle.

Lately ads have mocked President Obama for his comment that "the private sector is doing fine." "How can he fix the economy if he doesn't know what's wrong?" the ad says.

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While the Koch brothers are exceptionally private, they took a rare step onto the public stage in March when they sued the Cato Institute, a libertarian refuge in Washington that they helped create, for more control. The result was a public debate over Cato's role, and even as the brothers denied that they wanted to turn the think tank into an arm of the Republican Party, libertarians quickly sided with the group over the brothers. One senior policy fellow at Cato predicted that if the Kochs were to take control, the group's chairman and half the staff would eventually leave.

Obama, too, has tried to inspire his supporters by deriding the Kochs. In February, Obama's campaign manager, Jim Messina, sent a fundraising note to supporters accusing the Kochs of "jacking up prices at the pump." In a letter from a spokesman, the Kochs denied both the charge and a claim that they were pledging to spend hundreds of millions of dollars targeting Obama.

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Critics of the Kochs' business, Koch Industries, also point to a revelation that a subsidiary of the company traded with Iran, and that another paid bribes around the world. The Kochs' company said it follows the law and called the claims, in a Bloomberg Markets report, a result of "substandard reporting."