I see a lot of people saying that the language of the 14th Amendment is clear. I have to admit that I was once in that crowd but now I'm not so sure it's all that clear.
The issue is the clause "subject to the jurisdiction thereof."
What exactly does that mean? In 1898, the SCOTUS in US v. Wong Kim Ark ruled that the phrase "subject to the jurisdiction thereof" included all native-born children except for those who were: (1) born to foreign rulers or diplomats, (2) born on foreign public ships, or (3) born to enemy forces engaged in hostile occupation of the country's territory.
Elk v. Wilkins from 1884 was also still in effect, and would be until 1924, in which the Supreme Court found that Native Americans were not citizens by birth under the Fourteenth Amendment.
Chinese were a special case because the Chinese Exclusion Act, which prohibited Chinese from entering the country or being naturalized, was still in effect. However Chinese that were already in the country prior to the Exclusion Act were legally permitted to stay and Wong's parents had been in the country since before the Exclusion Act was passed. Because they were legally permitted to stay, the court ruled that they were "subject to the jurisdiction thereof" of the United States.
Do we all see the problem here? Illegal immigrants are arguably not legally "permitted to stay" and this might be enough of a hook for the SCOTUS to further limit birthright citizenship.
I also think a good case can be made that temporary visitors owe allegiance to their country of origin and therefore are not "subject to the jurisdiction thereof" of the United States.