The Romney campaign won’t release the list of his campaign finance bundlers, even though George W. Bush did, John McCain did, and Barack Obama did last time and is this time.

But thanks to some crucial investigative work by Dan Eggen and the Washington Post team, we now have a much better picture of his fundraising apparatus:

In Illinois and around the nation, Romney has built a web of campaign bundlers and other top fundraisers that stands to rival Obama’s, with more than 500 supporters who have raised at least $10,000 for the campaign, according to a review of fundraising invitations, state finance committee lists and other reports.

The top ranks are dominated by hedge-fund managers, bank executives and other members of the financial industry, along with a significant number of energy executives, real estate developers and other business owners, the review shows. The numbers are imprecise because, unlike Obama, Romney has declined to release a list of his top bundlers, who host fundraising events and help collect checks for the campaign.

More than three dozen of Romney’s biggest fundraisers are in the financial hub of Chicago, where a cross section of the city’s business elite has rallied around the former private-equity manager as the best candidate to beat Obama in the fall.