This is just his own big idea.
In any case...how are we supposed to determine when he is serious about something, and when he is just saying something for effect or as a retort?
@Maj. Bill Martin Demand to see the video of the speech...for needed context. Or a audio track AND transcript from a reliable source/link

Just recently, Pres. Trump got into character at one of his events mocking the suggestion that he should hire an Attorney General who will indict all his political enemies.
That didn't stop Nancy Pelosi saying to Anderson Cooper on CNN..."Well that would be a Banana Republic...without the banana!" (acknowledging that the USA is at least a decade away from being a REAL Banana Republic)
That's right. That BLEEP had the gall to phrase the question to Pelosi as Pres. Trump actually promising/stating that would be his intent...to indict and arrest everybody that went after him.