Nominating a former Assistant Attorney General at the Department of Justice means sending up an individual who has been through Senate confirmation once before and thus at least partially vetted.
A Justice Patrick would add to the diversity of the court, which the left loves, and this also helps immunize the nominee from attacks.
Governor Patrick is a very intelligent, very articulate and accomplished man of the left. He is also in deep political trouble in Massachusetts, where his defeat in November would not only be an embarrassment to the president and the Chicago team that elected both Obama and Patrick, but which would also imperil Massachusetts’ redistricting.
The president wants another reliable, left-wing vote on the Court. Governor Patrick gives it to him.