The key language in the 14th Amendment is "and subject to the jurisdiction thereof" the interpretation of this language has long been debated. Subject to the jurisdiction in one sense means that the person has a loyalty or obligation of citizenship to the United States. For instance, most countries define birthright citizenship by "blood" so for instance a child born to two Mexican citizens is also a citizen of Mexico regardless of where the birth occurs. The 14th Amendment was designed very strictly speaking to insure that children born of former slaves were conferred automatic citizenship. The question is whether children born on US soil are "subject to the jurisdiction". I do not proffer an opinion as to what is best but the argument that Trump is seeking to repeal the 14th Amendment rather than applying a "traditional" interpretation of that phrase is hyperbole at its finest.