Democrats love to complain about gerrymandering, but they sure don’t hesitate to deploy it to maximum effect. Case in point is New Jersey, where the Democratic Legislature is trying to lock in one-party rule by essentially enshrining it in the state Constitution.

New Jersey has 40 districts that elect representatives to the state Senate and the General Assembly. Each decade after the U.S. census, the task of drawing new lines falls to a 10-person commission, with five members picked by each party chairman. When the two sides...