My grandfather always used to say, figures don't lie but liar's figure.

Mayor Bloomberg is an independent. We know nothing else so lets run with it:

http://www.newsmax.com/archives/ic/2007/6/26/105427.shtml

So their argument is:

While you might expect that Bloomberg entering the race will hurt Republicans, it will actually hurt democrats.

And there evidence is:

Polls show that The margin by which Clinton would win over Giuliani would widen with Bloomberg entering the race. WIDEN!... Excuse me, I must use the restroom.