From an unexpected quarter. The Supreme Court has ruled against Washington State in its suit regarding faithless electors. The decision was unanimous, and the opinion held in part

Nothing in the Constitution expressly prohibits States from taking away presidential electors’ voting discretion as Washington does[.]

And

The Constitution’s text and the nation’s history both support allowing a state to enforce an elector’s pledge to support his party’s nominee—and the state voters’ choice—for president[.]

That’s a reflection of our Constitution’s 10^th Amendment and an affirmation of textualism, and that’s what makes it surprising, coming as it does from the ruling’s author, Justice Elena Kagan.