The fact that they blatantly say they would deport people who are legally residing in the US (just because they don't like the law) is so absurd that it shouldn't be acceptable in a political campaign but here we are. If they can do that, they can then say "this green card you have was obtained using the law we don't like so we'll deport you too", and also "this citizenship you got is based on the law we don't like so off you go", and also "don't matter that you're born here because we don't like your parents so go to Mexico", and you can tell from the current attitude among their supporters that all of that would be perfectly normal and valid to them.
What comes after what I put in bold perhaps an exaggerated assumption on your part. In any self-respecting democracy you cannot be retroactively wronged. They can benefit you retroactively but not harm you.
In this case, for example, if Kamala wins and plays on January 20, she could retroactively give citizenship to all the people who are in an irregular situation in the USA (and/or who meet certain criteria, it is just an example).
But Trump could not take away the citizenship of someone who has it because his parents are from Mexico. He could propose in the future a law, or a reform of the constitution, according to which nationality would not be granted in such cases.
Nor would I like to focus the debate exclusively on the immigration issue. In another thread you criticized lowering taxes on billionaires and said you wouldn't mind across-the-board tax cuts as long as there were no what you called loopholes such as dividends and capital gains for the wealthiest. Would you like us to comment on this aspect?