Yesterday, Newark, New Jersey Mayor Cory Booker (D) attacked the Obama campaign for making an issue of Mitt Romney’s tenure at Bain Capital during an appearance on Meet the Press. While the progressive leader later backed off the criticisms, Republicans have been quick to highlight his comments as an attack against the idea that scrutiny of Mitt Romney’s record as a businessman is fair game.

A ThinkProgress examination of New Jersey campaign finance records for Booker’s first run for Mayor — back in 2002 — suggests a possible reason for his unease with attacks on Bain Capital and venture capital. They were among his earliest and most generous backers.

Contributions to his 2002 campaign from venture capitalists, investors, and big Wall Street bankers brought him more than $115,000 for his 2002 campaign. Among those contributing to his campaign were John Connaughton ($2,000), Steve Pagliuca ($2,200), Jonathan Lavine ($1,000) — all of Bain Capital. While the forms are not totally clear, it appears the campaign raised less than $800,000 total, making this a significant percentage.

He and his slate also jointly raised funds for the “Booker Team for Newark” joint committee. They received more than $450,000 for the 2002 campaign from the sector — including a pair of $15,400 contributions from Bain Capital Managing Directors Joshua Bekenstein and Mark Nunnelly. It appears that for the initial campaign and runoff, the slate raised less than $4 million — again making this a sizable chunk.

In all — just in his first Mayoral run — Booker’s committees received more than $565,000 from the people he was defending. At least $36,000 of that came from folks at Romney’s old firm.