Would that make everything that came from his administration, invalid?
If a challenge to his presidency is taken before the appropriate legal venue, whether that be judicial or congressional, and Arthur’s administration is legally invalidated due to the issue of his natural born citizenship, then to the extent that it can be it would have to be unraveled. Since so much time has elapsed, I would have no objection to that finding being mooted. But not in the case of the current administration. The legal challenges existed before he ever took office, and he did his best to stonewall them.