Changing the 14th Amendment?
Trump, as president, can reinterpret the application of one part of the 14th Amendment — an amendment meant to extend equal rights to former slaves which has been used to extend citizenship to children of illegal immigrants born in the U.S. (birthright citizenship). The amendment is arguably being used to do something it was never intended to do, so reinterpretation is welcome.
However, there is reason to suggest Congress, not the President, should be the first to reinterpret it.
If Trump issues an executive order to end birthright citizenship, Congress or the Supreme Court can overturn him. It remains an open question whether Trump will issue the order, and what Congress or the Supreme Court will do.