In recent days, President Donald J. Trump has floated the idea that he can end birthright citizenship with an executive order, stating, “It was always told to me that you needed a constitutional amendment. Guess what? You don’t.”The concept and arguments are not new ones. For example, when former Democratic Sen. Harry Reid, D-Nev., was majority leader, he supported legislation that would have done something similar.In recent days, Reid issued a statement that said his wife immediately set him straight …