And, actually, a case of US-born offspring of persons in the country illegally has never been tested before the Supreme Court. Furthermore, whatever the Constitution says, Trump is right on the merits: Not a single European nation has US-style unconditional birthright citizenship, and no Asian or African nation has it at all.
Australia: at least one parent has to be an Australian citizen or legal resident;
France: at least one parent has to be born in France;
Ireland: at least one parent has to be an Irish or UK citizen, or a permanent resident;
New Zealand: at least one parent has to be a New Zealand citizen or permanent resident.
Get the picture? There’s no point to American exceptionalism if it just means exceptionally suicidal.