Is a baby who is born in the U.S. a citizen?

Yes, a baby born in the U.S. is a U.S. citizen. It does not matter where the baby's parents were born. This is the law for the whole country, and it is part of the U.S. Constitution. It is called "birthright citizenship."

What does the U.S. Constitution say about birthright citizenship?

The Fourteenth Amendment to the Constitution says that "all persons born or naturalized in the United States…. are citizens of the United States and of the state where they reside."  

Can the President or Congress change the Constitution?

To change the constitution, Congress has to pass a new constitutional amendment. That requires a two-thirds vote in both the House of Representatives and the Senate. Then three-quarters of the states would have to agree with the new amendment. 

What about the President's "executive action?"

An announcement or executive action by the President does not change the constitution.