I think a Bloomberg candidacy has to help Mitt Romney, because it means the arrival in the race of hundreds of millions of dollars in independent expenditures.  The Democrats will have the Soros network working for them to help counter the impact of those dollars, but the GOP has nothing like the 527s of the left.  Not only does Romney have the best fund-raising network --by far-- he also has considerable personal wealth at his command, and --crucially-- a network of entrepreneurs and experienced and successful investors who believe enough in his abilities to form the sort fo 527s that would level the financial playing field.  The other two serious candidates, Giuliani and Thompson, do not have these assets and have not demonstrated the sort of network of extremely wealthy and motivated individuals who will match the Soros outlays. Perhaps Rudy has a similar network, but I haven't seen any evidence of it.  Thompson almost certainly does not.

Pragmatic Republicans have to realize that Bloomberg's entry makes the financial dimension of the campaign much more important, and that favors Romney. So too will the reactions of down ticket Republicans across the country worried about getting swept away in a sea of Clinton-Bloomberg left-wing ads and internet activism.  The Romney finanicial advantage and his management experience becomes a very compelling draw for those in the party who see a rough year ahead made even more turbulent by the approach of Bloomberg's billions.