The decision to mobilize the D.C. National Guard — by Secretary McCarthy and Christopher C. Miller, the acting defense secretary — came as a pro-Trump mob breached the Capitol earlier in the day.

Defense and administration officials said it was Vice President Mike Pence, not President Trump, who approved the order to deploy the D.C. National Guard. It was unclear why the president, who incited his supporters to storm the Capitol and who is still the commander in chief, did not give the order.