Donald Trump's national security adviser Michael Flynn has resigned less than a month into the role, after reports emerged that he had misled Vice President Mike Pence and other high-ranking officials about his contact with Russia.
Mr Flynn was revealed to have held a conversation with a Russian diplomat about sanctions prior to the inauguration of Donald Trump.
In his resignation letter, he admitted giving Vice President Mike Pence "incomplete information" about his calls with the Russian ambassador to the United States.
Mike Pence had initially said that the national security adviser had not discussed sanctions with the Russian ambassador.
Mr Flynn later conceded the issue may have arisen, in his resignation letter:
Unfortunately, because of the fast pace of events, I inadvertently briefed the Vice President Elect and others with incomplete information regarding my phone calls with the Russian Ambassador. I have sincerely apologised to the President and the Vice President, and they have accepted my apology.
Breaking: text of Flynn's resignation letter https://t.co/KGue1cJFzL
The White House has said it will replace Mr Flynn with retired Army Lt. Gen. Joseph K Kellogg Jr as acting national security adviser.
People have been quick to point out that Mr Flynn was an early and vociferous critic of then-Democratic Party Presidential candidate Hillary Clinton's private email server early on in Donald Trump's campaign.
During his appearance at the Republican National Convention, he led the audience in cries of:
Lock her up! Lock her up!
He told the crowd:
If I did a tenth of what she did, I'd be in jail today.
In July, an FBI investigation concluded no "reasonable prosecutor" would bring a criminal case against Mrs Clinton, a case that was opened and shut again the week prior to the US Presidential election.
Two days prior to the vote, FBI Director James Comey announced he was standing by his original assessment - that Mrs Clinton should not face criminal charges.