If a law is struck down as unconstitutional, isn't that prima facie evidence that the politicians who voted for, signed, and executed that law are failing to uphold their sworn duty to uphold the Constitution?

No, because a politicians job isn't to know the constitution inside out and uphold it - even though they should. That's generally the supreme court's job. What politicians do is to push forward whatever law (or amendments, or revision of previous laws, etc) the populace wants them to, so that's what they do - which may or may not end up being unconstitutional in nature or interpretation. As you may have noticed, that's what a lot of political campaigning and rallies revolves around: talking shit about what laws they would pass or would cancel.

This is a loaded question and it's biased bullshit. I mean this respectfully because I understand it may or may not be your supposition, as I've seen a lot of misguided people parroting this around for years and years.