US Transportation Secretary Elaine Chao announced her resignation on Thursday, the first cabinet minister to join a growing list of Republican President Donald Trump's staff leaving over the storming of the US Capitol by his supporters.
Chao, the wife of Senate Majority Leader Mitch McConnell, said the mob attack "has deeply troubled me in a way that I simply cannot set aside." She said her resignation will take effect on Monday.
Deputy national security adviser Matt Pottinger, a leading figure in the development of Trump's China policy, resigned abruptly on Wednesday, said a senior administration official who declined to be named.
He was followed by Ryan Tully, senior director for European and Russian affairs at the National Security Council, a second senior official said, on condition of anonymity.
Trump's pledge on Thursday that there would be an "orderly transition" to the presidency of Democrat Joe Biden on Jan. 20 was partly intended to head off further resignations, but the second official told Reuters: "It's not going to stop it." With two weeks left of Trump's presidency, many aides were already heading for the door, but the sudden departures suggested revulsion among some over his encouragement of mobs of supporters who stormed the Capitol in an ultimately futile bid to prevent formal certification of Biden's election victory.
The images filled television screens in the United States and around the world, forever marking Trump's presidency and legacy.
Chao, a labor secretary and deputy transportation secretary under previous Republican presidents, has led the department for four years.
In an interview with Reuters on Dec. 31, Chao had said she planned to remain on the job through Jan. 20.
On Thursday, she was at pains to say that "we will help my announced successor, Mayor Pete Buttigieg, with taking on the responsibility of running this wonderful department." Among those who were spurred to quit on Thursday was Mick Mulvaney, a former White House chief of staff who resigned his post as a special envoy to Northern Ireland.
"I wouldn't be surprised to see more of my friends resign over the course of the next 24 to 48 hours," he said on CNBC.
Further departures are especially likely at the NSC, one of the officials said. It coordinates US foreign policy among federal agencies and maintains close contacts with foreign governments, so the loss of key staff could raise questions about national security as the new administration takes over.