Donald Trump has raised the stakes in an ongoing feud with the spouse of one of his closest advisers – describing him as a "loser" and the "husband from hell".
George Conway, the partner of White House aide Kellyanne Conway, has long criticised the US president – accusing him of lying and even claiming that Mr Trump is mentally unfit for office.
Following a barrage of ill-tempered tweets sent by Mr Trump over the weekend, Mr Conway accused the president of having narcissistic personality disorder.
The president replied: "George Conway, often referred to as Mr. Kellyanne Conway by those who know him, is VERY jealous of his wife's success & angry that I, with her help, didn't give him the job he so desperately wanted. I barely know him but just take a look, a stone cold LOSER & husband from hell!"
Mr Conway then posted a brief response of Twitter, simply writing: "You. Are. Nuts."
In 2017, it was reported that Mr Conway was in the running for a job at the Department for Justice, but he later withdrew himself from contention. The president insists the lawyer was actually turned down for the role.
Following Mr Trump's latest Twitter outburst, Mr Conway told Reuters: "The president seems determined to prove the point I've been making."
More from Donald Trump
It is unprecedented in Washington for the spouse of an aide to criticise the president so publicly.
The White House has largely stayed out of the public feud due to Mrs Conway's role in the government, but the president's son Eric did wade in in December – calling Mr Conway's actions "horrible".
In an interview with The New York Times this week, Mr Conway said he uses Twitter to air his frustrations so that he does not argue with his wife when she gets home.
He has also denied that he and his wife have a book or movie deal about their unusual situation – describing such a suggestion as "absurd".
The lawyer refused to comment on whether his spat with the president has affected his career or his marriage.
In an interview last year, Mrs Conway said she does not agree with her husband's analysis of the president.
She also told the Washington Post that Mr Conway's anti-Trump stance was disrespectful to her, adding: "It's a violation of basic decency, certainly, if not marital vows."