Dave Hardy has a post up on the substantial donation made by Mayor Mike Bloomberg to the Joyce Foundation. The money comes from his Bloomberg Philanthropies. At the same time as Bloomberg is giving money to the Joyce Foundation, the Brady Campaign is running a substantial deficit.
Sebastian examines this pattern of donations in more detail noting that little of the Bloomberg money is going to the more established (and somewhat more moderate) Brady Campaign/Center.
Essentially what Bloomberg is doing is to use the Joyce Foundation as a cut-out to fund the radical gun prohibitionists at CSGV, VPC, and Media Matters. The clamor from these organizations makes Mayor Bloomberg's Illegal Mayors aka MAIG look much more moderate and "reasonable" by comparison.
Read both sets of posts from Dave and Sebastian to understand the full impact of Bloomberg's moves.