From the Document: "On May 13, 2020, the Supreme Court is set to hear two cases, 'Chiafalo v. Washington' and 'Colorado Department of State v. Baca,' that could determine how much power states have to control the presidential selection process in the Electoral College. As a formal matter, the Constitution provides that state legislatures shall direct the appointment of presidential electors, who, in turn, cast ballots for President and Vice President. But in practice, every state legislature has determined that electors should follow the will of their state's voters. The question in these cases is whether states may 'require' electors to cast ballots for the presidential ticket favored by their voters, or whether electors retain the ultimate discretion to cast ballots for the candidates of their choice."
CRS Legal Sidebar, LSB10462
Congressional Research Service: https://crsreports.congress.gov/