The states are required by the Constitution to cast their electoral votes by Dec 14th. If there are contested states and neither candidate has 270 electoral votes, the Constitution calls for a vote of the House legislature, one vote per state delegation, on January 5th when they reconvene. If all the Republican states vote for Trump, he wins. If 4 defect, Biden wins. (26 republican legislatures vs 22 Democrat)
Trump is also well aware of this too as he mentioned it in a previous rally.
http://www.youtube.com/watch?v=LCW45stUbe8&t=47m55s
Skip to 47:55 on the video to see
For this to work, the people need to get out there and make their voices heard. Make sure the that it's very clear who the people want the states to vote for. No defectors.