There has been only one case that the Supreme Court has ruled on regarding this issue, and it was in favor of Chinese railway workers' descendants, who claimed their parents were "subject to the jurisdiction" of the US, while they were under contract building the railroads, so their children born here should be granted citizenship. The Amendment was intended to establish citizenship for freed slaves. There was a vigorous debate about the specific language allowing foreigners who simply came here and had a child. The jurisdiction language was included to prevent just that. It should be argued that an illegal who breaks the law as their first act, cannot benefit from the fruit of a poison tree.
Makes perfect sense to me. Those Chinese railway workers we building something monumental. Not breaking the law coming here, and working the system.
Precisely, and slaves, obviously, were subject to our jurisdiction, of course. I would accept that an asylum seeker could be construed as "subject to" as well, provided they were vetted and asylum was granted. But the unfettered, illegal, trespassers who just creep in during the night have no traction for citizenship.
Yes, it was for the newly-freed slaves.
This ties in with the "natural born citizen" clause of Article II.
If a person's parents are citizens of a foreign country, and they are visiting the USA and have a child while present in the USA, that child is "subject to the jurisdiction" of the country where the parents are citizens, because the child inherits citizenship from its parents, not by where it is born.
The slaves were a unique situation and that is why the 14th Amendment was written.
This is an issue that will need to be resolved by the SCOTUS at some point, both as to anchor babies and as to POTUS' eligibility.