Mick Mulvaney, a former chief of staff in Donald Trump's White House, announced Thursday he has quit his diplomatic post to protest mob violence by the president's supporters at the Capitol.
"I can't stay here, not after yesterday. You can't look at that yesterday and think I want to be a part of that in any way, shape or form," Mulvaney told CNBC television.
Mulvaney, who had been moved from chief of staff to special envoy for Northern Ireland, said he told Secretary of State Mike Pompeo he was resigning.
"I can't do it. I can't stay," he told CNBC, indicating that other White House staff were eying the exits.
"Those who choose to stay, and I have talked with some of them, are choosing to stay because they’re worried the president might put someone worse in," he said.
On Wednesday, thousands of Trump supporters left a rally with the president, then stormed into Congress, temporarily halting proceedings to certify Democrat Joe Biden as the winner of the November presidential election.
Immediately after the violence, which Trump has still failed to condemn, deputy national security adviser Matt Pottinger resigned.
Another departure was Stephanie Grisham, a former White House press secretary now working as spokeswoman for First Lady Melania Trump.
US media reported that Marc Short, chief of staff to Vice President Mike Pence, had been blocked from entering the White House -- apparently in retaliation for Pence's decision to ignore Trump's demand that he block the certification of Biden.
The outrage across Washington at the day's events fed growing speculation that more senior Trump administration figures may be leaving.
Biden will take over the presidency when he is sworn in on January 20.