Tomorrow Mitt Romney will speak at the Michigan Prosperity Forum, alongside Tea Party icons like Andrew Breitbart and Michelle Malkin. The event is sponsored by the conservative group Americans for Prosperity, which receives the bulk of its funding from the Koch brothers, whom the Romney campaign has described as “the financial engine of the Tea Party.”

It’s the third time Romney has appeared at an AFP gathering this cycle—he spoke before the group in New Hampshire over Labor Day and at their “Defending the American Dream” summit in November 2011. AFP, one of the main organizers behind the Tea Party, recently ran a $6 million ad campaign criticizing the Obama administration’s loan to Solyndra.

The Koch brothers, in turn, have been major supporters of Romney. David Koch endorsed him in 2008 and held a fundraiser for Romney at his Southampton home in 2010. Bill Koch and his coal company, Oxbow Carbon, have donated $1 million to the Romney Super PAC, Restore Our Future. At a recent retreat in California, David and Charles Koch pledged to spend $60 million during the 2012 election to defeat President Obama, which would no doubt give a major boost to Romney if and when he becomes the GOP nominee.

Romney’s estate tax plan alone could save the Kochs billions of dollars. His advocacy of the oil, gas and coal industries would also be a major boon to the Koch brothers’ many energy interests.

The Obama campaign is already using Romney’s Koch connections as a fundraising appeal, writing in an email today: “Tomorrow Mitt Romney is hanging out with the billionaire Koch brothers at a Tea Party forum. I imagine they’ll get along.”

Ari Berman is the author of Herding Donkeys: The Fight to Rebuild the Democratic Party and Reshape American Politics, out now in paperback.