What makes someone a US citizen?

[Whack-a-Mole]

This thread may be worth reading on this topic:

What is the legal reasoning that 'allows' ending birthright citizenship?

Please, no snark, no ‘trump is bad’, etc. I’m interested in what the legal argument is that the Trump administration is using to justify ending birthright with an executive order vs. a constitutional amendment. What is the legal wrangling they are using to think that an executive order is a legitimate means to accomplish the end goal?