I read on https://amp.theguardian.com/us-news/2020/jan/22/trump-travel-ban-visa-social-security-medicare (mirror):
The Trump administration has been restricting all forms of immigration, but the president has been particularly exercised by the issue of birthright citizenship – anyone born in the US is considered a citizen, under the constitution. He has railed against the practice and threatened to end it, but scholars and members of his administration have said it’s not so easy to do.
Why would it be difficult to stop the practice of birthright citizenship in the United States?