During a discussion about national security at the Aspen security conference, on July 21, 2017, former CIA director John Brennan reaffirmed his support for Mueller and called for members of Congress to resist if Trump fires Mueller. He also said it was "the obligation of some executive-branch officials to refuse to carry out some of these orders that, again, are inconsistent with what this country is all about."[75] After the firing of Peter Strzok, a central investigator for Mueller, for alleged partiality, Senator Mark Warner, the Ranking Member of the United States Senate Select Committee on Intelligence in a speech on December 20, 2017 before the Senate warned of a constitutional crisis if the President fired Mueller.[76]