A majority of Supreme Court justices on Wednesday seemed reluctant to conclude that state legislators may manipulate congressional district lines and set federal voting rules without any oversight from state courts, after nearly three hours of debate over what would be a fundamental change in the way elections are conducted.

But some justices also indicated they believed state courts could be restrained from becoming too big a player in election decisions — at some point when “the state court would not be acting as a court but would be acting more as a legislature,” in the words of Justice Amy Coney Barrett.

Under the theory advanced by North Carolina’s Republican legislative leaders, state lawmakers throughout the country could have exclusive authority to structure federal elections, subject only to intervention by Congress. The “independent state legislature theory” holds that the U.S. Constitution gives that power to lawmakers even if it results in extreme partisan voting maps for congressional seats and violates voter protections enshrined in state constitutions. ...