The 14th Amendment: All persons subject to the jurisdiction of the United States who are born or naturalized in the United States, are citizens of the United States and of the state wherein they reside.
Notice the clause “subject to the jurisdiction of” in the 14th Amendment. A newborn baby isn’t subject to the jurisdiction of the government anymore than a banana is subject to the jurisdiction of the government. There are impossible things and if a newborn is a citizen by birthright and it’s parents are illegal immigrants, who will take care of the newborn? Will the mother hand it over to the government? Why would a mother do that? Who or what is responsible for a newborn? An illegal immigrant is breaking the law by being in the Unied States. How would a mother go about identifying herself as a citizen who is subject to the jurisdiction of the United States if she is not a citizen of the United States.
The Jurisdiction clause refers to the newborn. The 14th Amendment doesn’t apply to illegal immigrants because they are not subject to the jurisdiction of the U.S. so neither is their newborn.
If the mother of a newborn is a legal immigrant or a U.S. citizen then the newborn is subject to the jurisdiction of the U.S. because the mother is. That’s when the birthright citizenship is triggered.
There are exceptions to the birthright clause, e.g., a newborn whose mother is a diplomat or a spouse of a diplomat because they are not subject to the jurisdiction of the U.S. Their newborn is therefore not a citizen and that’s an exception to the 14th Amendment. There are other exceptions too so Trumps Immigration Position Paper regarding his position to withhold birthright citizenship to illegal immigrants is on sound legal ground.