Gary D. Robertson | Associated Press

The case could increase the power of state lawmakers over races for Congress and the presidency, as well as redistricting. It also could cut state courts out of the equation. The issue has arisen repeatedly in cases from North Carolina and Pennsylvania, where Democratic majorities on the states’ highest courts have invoked voting protections in their state constitutions to frustrate the plans of Republican-dominated legislatures.

Former President Donald Trump’s winning streak in U.S. Senate primaries is on the line Tuesday as voters in five states cast their ballots in midterm elections. Trump backed celebrity heart surgeon Mehmet Oz and state Sen. Doug Mastriano in Pennsylvania's Republican primary for U.S. Senate and governor, respectively.