Looks like he repurposed his old people into political advisors.
Looking at people's experience, one can see that a fair number moved over from Bloomberg Philanthropies or Bloomberg LP. Additionally, a number of staff served in various capacities in the Bloomberg administration during his tenure as Mayor of New York City. The campaign has also picked up staff from erstwhile presidential campaigns, particularly those of Kamala Harris and Steve Bullock. At the state level the approach seems to be one of building coalitions, including a sprinkling of people with experience in organized labor as well as those from the private sector. The campaign has opened around 150 offices across the country as of Feb. 11 (30-40% of these are listed below).