POTUS signs Executive Order ending automatic birthright citizenship. 2) Democrats sue. 3) first Leftist judge rules the EO "unconstitutional" based on the Wong Kim Ark case from 1898. 4) Appeal 5) Eventually gets to Supreme Court. 6) Either status quo or automatic birthright citizenship ends. Since it hasn't been seriously considered since 1898, I bet a new precedent will be set.
"Subject to the jurisdiction thereof" means a citizen of thr US. No citizen parents, no citizenship.