“The structure of the Constitution, as interpreted by this Court over our 230-year history, prohibits the states from interfering with the exercise of this plainly federal function,” said Lawrence Lessig, a Harvard law professor involved in both cases.

The Supreme Court ruled in 1952 that states do not violate the Constitution when they require electors to pledge that they will abide by the popular vote. But the justices have never said whether it is constitutional to enforce those pledges.

“The Electoral College is unbelievably important to the mechanics of how we select a president, but it’s almost a mystery. The Supreme Court has told us virtually nothing about it, and certainly, this Supreme Court hasn’t said anything,” said Tom Goldstein, a Supreme Court expert who co-founded the website SCOTUSBlog and argues frequently before the court.