The article does say that he and his administration do not believe that the use of the 14th in that way would be Constitutional. It is kind of weird to see an administration that doesn't just get a lawyer to write some bullshit justification as why something is Constitutional, but that seems to be the case.

“If you think you've got an inside track to absolute truth, you become doctrinaire, humorless and intellectually constipated." Saul Alinskey