In normal times, we might regard any vote as ethical. To participate in an election is to dignify oneself as a citizen with a voice, and to express with others the interests and values that guide the future of our land. But these are not normal times.
This is clear from the perspective of the candidates. During a normal campaign, both candidates take for granted that they will walk free after the election. One will be in the Oval Office; the other will go home. This year is different. One candidate, Donald Trump, knows that, should he not remain in power, he will descend into poverty, go to prison, or both. He can hold the ongoing criminal investigations at bay as long as he is president, but not thereafter. Trump owes hundreds of millions of dollars to his creditors and has no visible means to pay them back. As president, he can expect his creditors to wait; as a private citizen, he cannot.
If someone can maintain wealth and freedom only by holding onto power, that person will fight to hold onto power. Behind the ideologies and the propaganda, this is the core history of tyranny: government becomes the bodyguard of a gangster. Modern authoritarians such as Vladimir Putin have much to say about why they must remain in power, but the real issue is that they wish to die wealthy and in their own beds rather than poor and in prison. In authoritarian countries, the anxiety of the tyrant can be allayed by a promise not to prosecute the leader and his family, and to leave their bank accounts in peace. Because the rule of law still (more or less) prevails in the United States, no one can offer Trump such a deal. He is therefore in a fight for his life; from his point of view, he needs to spend the rest of it in the White House. His predicament might not be obvious to Americans, but people in authoritarian countries see it right away.
It is also unusual, in an American presidential campaign, for one of the candidates to admit defeat. Trump has a fine political mind, and he can read polls and the national mood as well as anyone. For months now, he has been signaling that he cannot beat Joe Biden in an election. When he tried to summon the armed forces to aid him in June, it was the gesture of a man who needed unusual forms of help. When he tweeted in July that elections should be delayed, he revealed that he did not think he could win them. Undermining the United States Postal Service, asking his supporters to vote twice, and saying that he will not accept the results: all of these are ways of saying that he expects to lose. His campaign has ignored swing voters, and the Republican National Convention made no attempt to reach the undecided. In the first presidential debate, Trump tried, as he has done for months, to delegitimize the election as such.