We need to keep reminding ourselves – a President is not a medieval King.
The only legal Constitutional way to Drain the Swamp would be for Congress to pass laws and repeal laws. Yes – That Congress! – the same one most of whose members are almost entirely focused on self-preservation and self-enrichment. I am afraid that only the coming economic collapse will lead to the draining of the Swamp.
In the meantime, if President Trump can wind down foreign wars, enforce US borders, and push for fair balanced trade (areas where he has some ability to act with less Congressional and Court obstruction), he will have done us all a great service.
You are correct. However, the recent overturning of the Chevron Doctrine by the Supreme Court offers a new route to overturning at least some administrative overreach. It may come down to many lawsuits by interested parties - especially from the right (taking a page from the left) - demanding review of prior rules which have overreached. There are many.