Bloomberg and his PR team picked a "sure thing" (a Dem Machine candidate, already backed by Rahm and Madigan).
His $2+ Million was the price he paid to have a DC press conference, where he can point to this (as yet unindicted, but under investigation) gun grabber from Chicago as proof that the NRA and its political influence to be DOA.
The word is, he guaranteed Rahm financial support in his upcoming presidential/vice presidential run in 2016. That's why nobody raised a stink when he carpetbagged his way into town and started messing with a Dem primary.
Of course the irony is that while he's in DC claiming that the Illinois legislature is defining our first concealed carry law, by appellate court order.