What’s the logical train of thought here?

It’s OK for a citizen to lose their rights if a political party exists that espouses views you don’t agree with and it’s possible someone related to that citizen may (or may not) have listened to those views?

I think the steelman version would be that the rights in question shouldn't exist. In that world view, the birthright citizenship granted by the 14th amendment is an inconvenience to be worked around; and the business here about forcing a "choice"[1] where the parents will "deport" their own citizen children is in fact the desired policy result and not a humanitarian horror.

[1] Which of course isn't one, thus the Orwellian point upthread.

Yeesh. Even the steelman is grossly immoral!

The tired trope of blaming all bad Republican actions on Democrats because they "let it happen" is lame.

No, the democrats are not secretly worse because they're watching evil happen. The people doing the evil are worse, actually. That's just how that works.

What promise was that, exactly? Do you have a quote?

If not, and you mean “promise by inaction”, then could we say then that Trump made a promise to racists, neo-nazis, crypto criminals, the Russian government, etc?