Obviously an aggressive public relations campaign, led not only by Trump himself but also by lawyers Rudy Giuliani and Jay Sekulow, was a key. Trump never backed down from his insistence that he was innocent of all wrongdoing and that the whole was nothing but a witchhunt. In other words, as Devin Nunes said yesterday in response to the question, When did Mueller know he had no case:
"Likely since [the moment] he walked in the door [took charge] of the phony investigation."
A correspondent has sent me a Reuters article that addresses the question of Trump's successful resistance to an interview. Unfortunately, the article--The Mueller interview that wasn't: how Trump's legal strategy paid off--is short on legal analysis. My view, which shouldn't come as any surprise, is that the lack of probable cause for a legitimate investigation was key.
Consider: Team Mueller was only authorized to investigate an alleged conspiracy to collaborate illegally with Russian intelligence operatives--an alleged conspiracy that was supposed to have been conducted by an "enterprise" group of "four Americans" (Page, Papadopoulos, Manafort, and Flynn) as a subset of the Trump campaign. That was Crossfire Hurricane, which Team Mueller was authorized to continue. That means that, just as James Comey three times stated to Trump, Trump was never actually the subject of the substantive investigation:
