“The only reason to challenge it is to get it into the courts to determine the constitutionality of the existing law. Trump can do it thru an Executive Order or Congress can do it by passing a bill signed by the President.”
I really cannot see President Trump taking such a stance or action.
There are only about 30 countries in the world that have birthright citizenship with most of them being in the "New World." The only developed countries to have it are the US and Canada. Mexico also has it.