One may refrain from voting for POTUS altogether.
One may vote for Eternal Vigilance (Tom Hoefling).
One can vote for other worthy candidates (ABR/ABO).
One can write in, although most write-ins won't be counted.
In any event, one can and should pray, repent, and rely on Almighty God to protect this badly wounded nation (as He has so often in the past) in its time of need. If the survival and moral prospering of this nation is not in God's plan, we won't be the first nation nor likely the last to suffer such a fate and we cannot very well say that we did not deserve to go the way of so many dead punished nations. It is utterly amazing that God has put up with us as long as He has.
“There remains the one standard that has not yet been universally used, namely, the choosing of candidates on moral grounds. A nation always gets the kind of politicians it deserves. When our moral standards are different, our legislation will be different. As long as the decent people refuse to believe that morality must manifest itself in every sphere of human activity, including the political, they will not meet the challenge of Marxism. Contemporary history proves that modern political leaders, devoid of a moral inspiration and relying solely on a mass basis (might makes right), proves ineffectual in time of crisis."-- Fulton Sheen, “COMMUNISM and the CONSCIENCE of the WEST” -1948