Part of the rules to be aware of, and an option...
To the best of my knowlege, the chosen elector votes for the person he chooses. They are, of course, pledged to support a particular candidate, but if they change their mind, their vote still counts!
So, even if said electors are in violation of state law, and go to jail, the results still stand.
So...there's a close election. The Democrats should have won, but a spoiler candidate draws enough votes to hand some key states to the Republicans, and wins one state outright. (Or perhaps gets ONE electoral vote, by winning in one senatorial district in Maine.) <Of course, it's just as easy for the Democrat and Republican roles to be reversed>
Normally, Republican presidency ensues. But, after the election in November, but before the electoral college meets, the candidate is utterly disgraced by a scandal of epic proportions, one that makes Watergate look minor. At the same time, the Democratic candidate is assassinated. Both VP candidates are considered poor choices..strictly "balance the ticket" candidates. One is part of the radical right, the other part of the radical left. The country is in turmoil already...war, depression, energy crunch, or some other mess, and no one wants either of them in ofice in desperate time. The college debates, and finally chooses the third party candidate. It helps if the third party candidate is someone both sides can at least respect, and consider competent. More likely if the democrat and republican candidates are towards the extreme ends of their respecitve parties.
Now, the electoral college has done its duty, presented Congress with a clear winner...it's a done deal.