The Supreme Court is weighing a theory that could upend elections. Here's how

A sign held up by a demonstrator says "MOORE V. HARPER: A WEAPON TO OVERTURN ELECTIONS" at a December rally outside the Supreme Court in Washington, D.C. (Mariam Zuhaib/AP)

Some watchers of the U.S. Supreme Court breathed a sigh of relief last month after most of the justices sounded skeptical during oral arguments about a once-fringe legal theory that could upend elections across the United States.

Still, many legal scholars and voting rights advocates remain on alert for a court ruling by this summer on what's known as the "independent state legislature theory." It claims that under the U.S. Constitution, state legislatures have the power to determine how federal elections are run, without any checks or balances from state constitutions or state courts.