On December 19, the Electoral College meets to elect our next president. The Electoral College was conceived by James Wilson as a compromise at the Constitutional Convention to alleviate concerns that the general electorate was beholden to local interests or susceptible to “talents for low intrigue, and the little arts of popularity” (Hamilton). Hamilton also wrote that “The process of election affords a moral certainty, that the office of President will never fall to the lot of any man who is not in an eminent degree endowed with the requisite qualifications.”
The upshot is that it is not only constitutional for the Electoral College to vote their conscience, it is their obligation and the original goal of the framers for them to do so.
Counterpoint: What would a Electoral College revolt do to our democracy? Try reading a dissenting opinion at this Economist opinion piece, which argues that while an Electoral College revolt is what the framers had in mind, it argues that either the Electoral College is a bad idea, or our implementation of it is flawed, but that a revolt is a threat to our democracy.
For an interesting perspective from a Republican elector who has vowed to not vote for Trump, read this NY Times op-ed piece.
For an even more interesting take, read this Washington Post opinion piece which argues that the most promising way for Democrats to stop Trump would be to elect a more moderate Republican like Mitt Romney. How does that work? Hillary Clinton needs to release all of her pledged votes and direct them to vote for Romney (for example). Then, only a small number of Republican pledged electors would need to join in to give Romney the majority.
President Romney, anyone?