There's a federal v. state split on that they'll resolve. Colorado and Washington are two states that can, under their state law, impose punishment to faithless electors. Washington state said it was fine, the 10th circuit said it was unconstitutional for Colorado to do so. Here's the petition for writ that they granted if you want a deep dive into the weirdness of faithless electors.
https://www.supremecourt.gov/DocketP...Certiorari.pdf
Of course, faithless electors are very rare, but, they could theoretically swing an election. There were 7 Dem electors that didn't vote for Clinton in 2016, though, I'm sure they would have if that would have made a difference in the election.