Christopher Miller, seen at a Senate hearing in September, was named acting defense secretary on Monday as part of President Trump’s shake-up of the national security community.

(L-R) FBI Director, Christopher Wray; National Counterterrorism Center Director ,Christopher Miller; and Deputy Homeland Security Secretary, Ken Cuccinelli, are sworn in before a Senate Homeland Security and Governmental Affairs Committee hearing on “Threats to the Homeland” on Capitol Hill in Washington, DC, on September 24, 2020. (Photo by Tom Williams / POOL / AFP) (Photo by TOM WILLIAMS/POOL/AFP via Getty Images)