Through what power? For instance, by legislative power or by decree.
Simply by practice.
The federal, state and local governments treat anchor babies as citizens. No one stopped this practice, so now it's accepted law.
Sometimes practice evolves into custom, and custom into law. Simply because no one put a stop to it.
If you don't know then just say so. Nobody will hold you to blame for your ignorance (lack of knowledge).
You're not stupid no matter what the Democrats want you to believe about yourself.
Sadly, "everybody knows that..." means most people don't have a clue.
Allow me...ArtI.S8.C18.8.1 Overview of Congress's Immigration Powers
And through that Consitutional power, Congress enacted USC 8 (ALIENS AND NATIONALITY) which includes CHAPTER 12—IMMIGRATION AND NATIONALITY.
That law, that Chapter and specifically Section 1401 of that Chapter, grants citizenship to chidren born of aliens who are born in the US. Once that birth certificate is done it's a done deal. Anchor baby!
8 FAM 300 U.S. Citizenship and Nationality
8 FAM 301.1 Acquisition by Birth in the United States
Do take the time to read that as well..Note that it is STATUTE (through laws) authority...
U.S. laws governing the acquisition of citizenship at birth embody two legal principles...
They're citizens with the same rights as natural born except for the right, and honor, to run for POTUS though their children may one day.
As always, JMO, YMMV