The US special envoy to Northern Ireland is resigning his post in protest at events in Washington DC on Wednesday.
Mick Mulvaney said he called US Secretary of State Mike Pompeo on Wednesday night to tender his resignation.
He also suggested that other officials may follow suit.
It follows dramatic scenes that drew international condemnation - including from the Taoiseach Micheál Martin and Foreign Affairs Minister Simon Coveney - which saw supporters of Mr Trump storm the US Capitol Building.
Four people died and more than 50 arrests were made.
Minister Coveney said the scenes were "a deliberate assault on democracy by a sitting President & his supporters, attempting to overturn a free & fair election".
On his resignation, Mr Mulvaney told CNBC: "I called Mike Pompeo last night to let him know I was resigning from that. I can't do it. I can't stay".
"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.
But he said that other officials may resign, adding: "We didn't sign up for what you saw last night.
"We signed up for making America great again, we signed up for lower taxes and less regulation.
"The president has a long list of successes that we can be proud of.
"But all of that went away yesterday and I think you're right to ask the question as to how did it happen".
It comes after Mr Trump finally conceded the November election and pledged an 'orderly transition' of power later this month.
Early on Thursday, he publicly acknowledged his term in office was ending - while insisting he 'totally disagrees' with the election result.
The statement came via a senior White House aide, as Mr Trump has been sanctioned by Twitter and other social media platforms for violating their rules.
"Even though I totally disagree with the outcome of the election, and the facts bear me out, nevertheless there will be an orderly transition on January 20th", the statement read.
"I have always said we would continue our fight to ensure that only legal votes were counted.
"While this represents the end of the greatest first term in presidential history, it’s only the beginning of our fight to Make America Great Again!"
