In 2016, there were 10 faithless electors, only three of which were invalidated according to Wikipedia.
Right now, it looks like Trump may lose with 268 to 270 electoral college voters (Trump: AK, GA, PA, NC). If Trump loses with 268 votes, ONE faithless elector sends the election to the House, where voting is one vote per State, and he wins.
What are the odds there will be a faithless elector? It’s still legal in most States, and there were 10 faithless electors, 7 of whose votes remained valid. Two electors switched from Trump, and several switched from Clinton. None of the electors switched from one major party candidate to the other, though.
Trump could also win by a recount, by an intervention from SCOTUS, or if Biden is claimed, in court, to be mentally incompetent, thus invalidating his presidency by a sort of 25th Amendment in advance (as a legal argument, not as a direct application of the Amendment).
So it’s not over until January 20th/21st, and maybe not even then.
RLCJ
the reproach of Christ 
Hi Ron, you speculated that a faithless elector might defect from Biden to Trump, thus changing the score to 269-269, and sending the election to the House. If there were instead 2 faithless Biden electors, but they defected to third party candidates instead of to Trump, thus leading to a 268-268 tie, would that have the same ultimate effect of sending the election to the House?
Yes.
What if the contingent of faithless electors chose to not vote for trump but all of the Democratic electors voted for Biden? Would Biden still win?
Then Biden would win. I don’t really want Trump to win by means of faithless electors. But I don’t believe Biden has won yet.