That would be an unlawful order to murder a civilian. The Seals would not follow such an order. NSA or CIA may follow a clandestine order.
Even if the order were carried out, a president can be impeached and removed, then tried in an Article 3 court. An impeachable offense is whatever the House deems impeachable. Trump was impeached twice on bogus charges. Didn’t matter. Impeachment is not subject to appeal. For better or for worse, the legislative’s branch impeachment and removal authority is the ultimate check and balance. No one is arguing presidents are immune, for any and all crimes. That’s a typical liberal red-herring. The Trump defense team is merely schooling the moron Obama, Clinton and Bush judges that the Constitution spells out what the process shall be to hold a lawless president accountable.