Nonpartisan means something isn’t partisan (duh) or biased toward one political group, so it’s a little odd to see the term applied to an organization made up entirely of Democrats and their operatives.
So it goes with Michelle Obama’s voter registration organization When We All Vote, which claims to be nonpartisan despite the fact that not a single known conservative, Republican, or Libertarian is anywhere to be seen. But the left-leaning media certainly wants everyone to think this organization is “nonpartisan,” as they keep stressing this in articles about the group.