Nope. You've retreated into you endless loop of electoral hypothetical again, where only two things are ever possible and you have to do one of them anyway. Without addressing the contradication at the core of it, which is why I asked you how you rationalised it.

The president is a bit of a special case, in that there's one of them, and of the two candidates

No it's not. There's more than two presidential candidates. And all elected positions are filled only by one eventual winner from the crop of candidates, just like literally every election. For someone preaching that the only possibility is electoralism in the narrowest term, you don't seem very knowledgable on, you know, actual elections, including the specific ones you're referencing.

anything that increases the risk of trump getting in, especially with a republican majority in one or both houses, is surely a bad idea.

And you can (and in some cases do) argue that anything short of voting for, capmapigning for, donating to, and never ever showing any disatisfaction with the Democrats qualifies as this. Why stop at withholding your vote? Or campaigning for change 'at the wrong time'? Have you been door knocking and phone banking for Biden? If not, why not? If you have, why aren't you doing it now, and in every spare moment, or quitting your job to do it full time? Have you donated every cent you own to the Democratic party? What about selling any property or other assets you have? Aren't you part of the problem?

(And that's just within your myopic electoral view, never mind non-electoral strategies from the common to the extreme)