Let me draw your attention to this new article in the Times, the subject of which is the range of rivalries, turf wars and personality conflicts which epitomize the Trump White House and are coming to the fore under the Stress Test of impeachment. One of these is the on-going battle between “acting” Chief of Staff and John Bolton, which flared up overnight when Bolton and his protege told Mulvaney to get his own lawsuit against the President and stop trying to glom on to theirs. Mulvaney complied. He first appeared set to file his own lawsuit before — apparently? — giving up on the whole idea.
But note this passage in the Times article which suggests that Mulvaney is telling colleagues he’s all but unfireable since he knows too much damaging information about President Trump.