There are two arguments I personally find persuasive. First, are you okay with having voted for a candidate that knowingly supported a genocide with words and with weapons (because it looks more and more like this is / will be the case). Second, what other leverage do you have over the Democratic party. Let them know that they can not win with such a historically shitty candidate, lick your wounds and try again next election.

And if you think Trump is literally Hitler, please do some research and look up what happened after Germany voted for the lesser of two evils (Hindenburg).