This Supreme Court case ruled that “unfaithful presidential electors” can be punished or replaced if they refuse to cast their ballot for the majority favored candidate of the state. The elector pledges to vote for the candidate that wins the state’s popular vote, but some choose to be discursive and vote independently. This document goes over the Supreme Court’s ruling and its broader implications for the electoral college.

https://crsreports.congress.gov/product/pdf/LSB/LSB10515