LONDON--U.S. President Donald Trump lashed out at "foolish" British Prime Minister Theresa May and her "wacky" Washington ambassador on Tuesday, stepping up a tirade against a close ally whose envoy had branded his administration inept.

  May has given her full support to Kim Darroch after he described Trump's administration as "dysfunctional" and "inept" in memos that were leaked to a British newspaper on Sunday.
  While ministers and May's spokesman have stated the leaked cables were only a partial reflection of Darroch's assessments and did not reflect the government's views, they have infuriated Trump, who fired off a second series of scathing tweets.
  "The wacky Ambassador that the UK foisted upon the United States is not someone we are thrilled with, a very stupid guy," Trump wrote, describing Darroch as a "pompous fool". "He should speak to his country, and Prime Minister May, about their failed Brexit negotiation, and not be upset with my criticism of how badly it was handled. I told @theresa_may how to do that deal, but she went her own foolish way - was unable to get it done. A disaster!"
  May is due to leave office this month and the spat with the United States divided the two contenders who are battling to replace her. Boris Johnson, the former London mayor and favourite to enter Downing Street as the next prime minister, said Britain's relationship with the United States was incredibly important.
  Asked in a television debate whether Darroch would retain his job under a Johnson government, he said he would not be so presumptuous as to think he would be in a position to take that decision. He then said it was not "necessarily" the right thing for Trump to have said, but added: "Let's face it, our relationship with the U.S. is of fantastic importance."
  Foreign Secretary Jeremy Hunt went much further, saying the comments were "disrespectful and wrong" to May and the country. "You said the UK/US alliance was the greatest in history and I agree," he said on Twitter. "But allies need to treat each other with respect as @theresa_may has always done with you. Ambassadors are appointed by the UK government and if I become PM our Ambassador stays."