Mortification only makes sense if you thought Trump and his supporters had principles to preclude this. It relies on an assumption that Trump is not totally lacking in respect for truth, peace, rule of law — anything, really, beyond his own wealth, power, comfort, and ego. Mulvaney’s apparent shock is only intelligible if he didn’t understand anything about the man he worked with for four years. And how could he not understand? How could he not know?
Mulvaney was first elected to Congress in 2010, the peak Tea Party year. He was a founding member of the House Freedom Caucus and palled around with people like former Rep. Justin Amash, who would later leave the Republican Party for reasons including its embrace of Trump, whose impeachment he supported. Mulvaney went dead in the other direction.
Perhaps he thought he could do some good. Perhaps leading the OMB seemed like an opportunity to slash the regulatory state in a way he could not achieve as a congressional backbencher. Perhaps taking on the duties of chief of staff seemed like an opportunity to restrain Trump’s worst impulses. Perhaps Mulvaney somehow thought he’d succeed where Reince Priebus and John Kelly failed. Perhaps all these hopes overwhelmed his ability to observe reality.