The government brief on birthright citizenship was submitted to the Supreme Court, in Trump v Barbara. Currently, birthright citizenship is 100% assured except in very limited circumstances, such as being a child of a diplomat. This virtually complete right is tied by courts to the 14th amendment which reads:
“All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside.”
The government brief takes a circuitous route to redefine “subject to the jurisdiction.” It introduces the term “primary allegiance” – the child must have primary allegiance to be subject to the jurisdiction. This term and its definition is not nailed down in past court decisions. The brief ties the term to immigration categories, such as illegal status, temporary status, adding another term “domicile.” If a child cannot claims domicile status, it is not given citizenship.
If one peels away these terms, one gets to a core, “originalist” interpretation, that Congress retains the right to create and quality immigration status categories and domcile and primary allegience, and thereby citizenship rights of newborns. Thus, for example, assume there is a 10-year working visa program. Congress could define this program in a way to deny citizenship status of children born to such parents.
Because this is fundamentally an originalist argument, there will be justics such as Thomas and Alito who will support the government’s position. Perhaps Barrett, Kavanaugh and Gorsuch. Hence, it could be a close vote and go either way.