US President Donald Trump landed in London for a state visit to the United Kingdom, which he kicked off by an angry exchange with London Mayor Sadiq Khan.

Khan was outspoken in his opposition to Trump’s visit, saying that the US President is not welcome and calling him to a “20th century fascist”. In return, Trump mocked Khan as a short person who allows crime in London to go unchecked.

Sadiq Khan, who by all accounts has done a terrible job as Mayor of London, has been foolishly “nasty” to the visiting President of the United States, by far the most important ally of the United Kingdom. He is a stone cold loser who should focus on crime in London, not me. Kahn reminds me very much of our very dumb and incompetent Mayor of NYC, de Blasio, who has also done a terrible job – only half his height. In any event, I look forward to being a great friend to the United Kingdom, and am looking very much forward to my visit. Landing now!, Trump tweeted.

The US President arrives at a time of political meltdown in the UK, where established parties suffered dramatic losses in the European elections in favor of more clearly positioned pro and anti Brexit parties, prompting Prime Minister Theresa May to resign. Trump endorsed Boris Johnson to become the next Prime Minister of the UK and to deliver a proper Brexit from the European Union.