Bloomberg is trying to create the impression that he is some kind of unstoppable political juggernaut; but he is mostly manipulating media to create a false impression.
In 2012, the NRA spent $20-24 million (depending on what you call a campaign expense) to elect 220 NRA A-rated House members and 40-something Senators. By contrast, Bloomberg CLAIMS to have spent $12 million on six House races to unseat three NRA B and C rated Reps. That is not a winning strategy and unless Bloomberg has a significant amount of his $27 billion in cash, rather than assets, it isn't a strategy he can afford to pursue.
In the election for Jesse Jackson Jr.'s seat, Bloomberg campaigned against a candidate who already faced a series of significant obstacles to getting elected. She was opposed by the Chicago machine and she was the only white candidate running for Jackson's Cook County district - which many thought a potential problem for her.
Depending on which source you believe, Bloomberg claimed to have spent $1.4 million, $2.1 million, or $3 million (I'd also note that as the story got older and bigger, the money claimed spent went steadily up) to make sure a candidate who was at best an underdog lost - and this wasn't a super pro-gun candidate, Halvorson supported registration and several burdensome gun laws. She simply opposed bans on guns and magazines. And for the record, Halvorson actually picked up a bounce in the polls after Bloomberg's big ad campaign.
It seems to me that whatever Bloomberg did spend to make sure Halvorson didn't win was more about creating a false narrative that he has millions and millions of dollars he will spend to defeat those who oppose him. Same with this announcement... Bloomberg can spend $500,000... Blanket the airwaves for a few days so that people actually see his commercial and then claim he spent whatever he thinks will scare the pee out of politicians and make them more pliable to hs will.
I don't think it is going to work; because ultimately Bloomberg can't buy votes - and his commercial isn't going to stir up some silent majority that supports gun control, by and large, it will anger and motivate gun owners to get involved and write. Whoever makes the mistake of listening to Bloomberg won't get a second chance to make it after 2014.