I don't know a lot about Bloomberg but I know progressives didn't like him all that much a few years ago. He has the luxury right now and the campaign smarts to define himself to the larger audience before someone else beats him to the punch. He's not a choir boy but for a party bent on anybody but Trump he may not have to be. I think he is for open borders and amnesty. He sees immigration as essential to economic growth and I think that covers both legal and illegal. He is the grandson of immigrants himself.
I just started looking into his "positions" but my first impression is that it's unlikely a lot of people on the left will fall in love with him. If they choose, many won't be voting for Bloomberg so much as they will be voting against Trump. I don't know if that will be enough but it could be. Obviously he's for gun control, abortion, and many of the left's positions. I don't know if the socialist label will stick to him as easily as some others.
https://www.mikebloomberg.com/getting-it-done
There has been talk in the past about Bloomberg running and the left usually mocked that idea. My argument to some of my friends on the left at the time was I thought he was a more sane option compared to what they were pushing. At the time it was thought he'd run as an independent.
At the moment I'm not sure Bloomberg will be able to generate any significant enthusiasm, at least not for himself. He's no Trump and he's no Bernie. He's no Obama nor is he a Reagan or Clinton. His main issue and strongest asset is probably his claim to having the best shot at beating Trump. That's it. I don't know if he can or not, not yet. To me he is the proverbial backup quarterback that comes into the game late with his team trailing and with the outlook bleak. He's a low 3-star at best but he has a lot of money and can hire a lot of smart people. He also, in the minds of some, may do far less down ballot damage than Bernie or others now contending for the nomination.
I think Trump probably described him accurately in a sense when he compared Bloomberg's persona to Jeb. His campaign is going to have to change that, I think, and the only way to do that may be to take a page or two out of Trump's playbook. Bloomberg needs to generate enthusiasm so he could start throwing out slogans like "Tear down the wall", or "Lock him up", things like that, and have his crowds, if he can muster any, enthusiastically chanting those refrains. He's probably a smart guy but I think he probably needs to dumb it down to take on Trump. jmo.
If Bloomberg runs a "Jeb styled" campaign against Trump, I suspect he'll come up "short". jmo.