The U.S. Supreme Court agreed (on January 20, 2020) to decide the constitutionality of laws in 32 states that purport to require members of the Electoral College to vote for their party’s presidential candidate. Washington Post article
After hearing the case (expected in April 2020), the Supreme Court is expected to resolve the conflict between two lower court decisions (probably in June 2020). See SCOTUS blog
In one of the lower-court cases, the U.S. Court of Appeals for the 10th Circuit in Denver on August 20, 2019 ruled, “states do not have the constitutional authority to interfere with presidential electors who exercise their constitutional right to vote for the President and Vice President candidates of their choice" (see page 93 of decision in Baca v. Colorado Department of State). The 10th Circuit decision resulted from a lawsuit filed after three Democratic presidential electors from Colorado refused to vote for Hillary Clinton when the Electoral College met on December 19, 2016. The Colorado Department of State removed the three electors as part of its effort to enforce a Colorado law requiring presidential electors to vote for their party’s presidential candidate. As the 10th Circuit itself acknowledged on page 67 of its decision, “The Supreme Court, however, has considered a closely analogous question -- whether a primary candidate for party elector can be required to pledge to support the party’s candidate.” In that case in 1952, the Supreme Court ruled in Ray v. Blair that state political parties could require presidential electors to pledge to vote for the party's nominees before being certified as electors. See documents in Baca case. Equal Citizens supports the 10th Circuit decision.
In the second case, the Washington State Supreme Court upheld the state's law requiring that presidential electors be faithful. The Washington State Supreme Court wrote (on page 15 of their decision in Chiafalo vs. State of Washington), "Ray supports the State's position that nothing in the plain language of either constitutional provision prohibits a state from imposing certain conditions on electors as a part of the state's appointment powers, including requiring electors to pledge their votes." See Chiafalo's petition to Supreme Court and State of Washington's brief
Eighteen states states do not have, and never have had, laws purporting to tell presidential electors how to vote. Moreover, laws that purport to require presidential electors to vote a certain way are of relatively recent vintage (all since the 1960s) in the states that have such laws. See map by FairVote.
The pending cases in the Supreme Court are not about the National Popular Vote Compact. The operation of the National Popular Vote interstate compact would not be affected regardless of whether the U.S. Supreme Court upholds the reasoning of the 10th Circuit or upholds the reasoning of Washington State Supreme Court, because the compact does not rely on state laws that purport to require presidential electors to vote a certain way. The compact does not try to tell presidential electors to vote a certain way. Therefore, the National Popular Vote organization is not planning to offer a brief on either side of this U.S. Supreme court case.
In fact, the National Popular Vote Compact would operate in a manner identical to the system that has been used for over 200 years in the 18 states that do not have laws requiring presidential electors to vote a certain way. In these 18 states (which currently use the state-by-state winner-take-all method of awarding electoral votes), the presidential electors are the persons nominated (in various ways) by the political party whose presidential candidate receives the most popular votes inside the state. The National Popular Vote Compact would operate in the same way, except the presidential electors would be the persons nominated by the political party whose presidential candidate receives the most popular votes in all 50 states and the District of Columbia.
Both the current system and the National Popular Vote system rely on political parties to vet and select their presidential electors. This system has worked reliably over the years in the 18 states that do not purport to tell their presidential electors how to vote. And, it has worked reliably in the 32 states before they adopted laws (all since the 1960s) that purport to tell presidential electors how to vote. After 23,529 electoral votes in 58 presidential elections between 1789 and 2016, the vote of Samuel Miles in 1796 was the only case when an electoral vote was cast in an unfaithful way by a presidential elector who might have thought, at the time he voted, that his vote might affect the outcome. See section 2.12 of Every Vote Equal book at www.Every-Vote.Equal.com
During the same period (1789 to 2016), there have been a number of "grand-standing" presidential electors -- that is, electors who have cast a deviant vote for President knowing, at the time they voted, that their vote would not affect the outcome of the election in the Electoral College. Prior to 2016, there had never been more than one grand-standing presidential elector in any given election. Having multiple faithless presidential electors in one year (2016) was unusual. All of the faithless electors in 2016 were well aware, at the time they voted, that their vote would not affect the outcome in the Electoral College because everyone knew that Donald Trump had won 36 more electoral votes than required for election.
Given the amount of publicity received by the grandstanding faithless electors in 2016, each political party can be expected to be extremely careful in 2020 about vetting the people they nominate for the position of presidential elector. If the political parties do their job of vetting their nominees for the position of presidential electors, faithless electors cannot have any effect on the outcome -- under either the current system or the National Popular Vote compact.
The increased attention on faithless presidential electors will probably cause many states to enact Pennsylvania’s law in which the presidential candidate directly nominates the people to serve as his or her presidential electors (25 P.S. §2878).