The birthright citizenship executive order looks like the legal equivalent of the Gaetz nomination–a deliberate provocation directed at the judicial system. What is Trump trying to do here?
From his perspective, he probably thinks he can’t lose. If his position is somehow upheld, he will know that the legal system has completely capitulated to him. If, as is more likely, the executive order is invalidated, he can scream about how the establishment is thwarting him again. He needs a foil to maintain his populist bona fides; the Supreme Court could very well do the job for him.
I don’t think he will defy this order if he loses. That is much more likely if the courts strike down one of his core deportation measures. Birthright citizenship, an abstract issue with few practical short-term consequences, is more of a trial balloon.