The London mayor claimed the US president’s behaviour was normalising and mainstreaming the abhorrent views of white supremacists and other extremists.
He made the comments in an interview on the American progressive politics podcast Pod Save America released on the day Mr Trump arrived in the UK for his state visit.
The war of words was sparked when Mr Khan described the US president over the weekend as “just one of the most egregious examples of a growing global threat” and compared the language he had used to that of the “fascists of the 20th century”.
Mr Trump hit back by mocking the height of the London mayor and calling him a “stone cold loser”.
Asked about his spat with the president, Mr Khan referred to Mr Trump’s ban on Muslims entering the US.
He said: “Donald Trump basically is the poster boy for the far right movement around the world.
“He and I first came into interaction when he decided he was going to ban Muslims from coming into the UK, apart from me because I’m the mayor of London.
“Banning Muslims from going to USA is a bad policy, it’s not the sort of America those of us who love America know.
“We have seen a number of policies which do cause concern to those of us in London, UK, Europe. The ripples of what is said by the president of the USA are felt all around the world.
“A number of things he has said and done is causing problems, people in France, Hungary, Italy, the UK ... who are having their views which are abhorrent normalised and mainstreamed because some of the things Donald Trump has done.”
Mr Khan said that progress in LGBT+ rights, gender equality and other policies was now in danger of “going backwards”.
“In the last 70 years we have not had a war in mainstream Europe so it does worry me that the right(-wing) part of politics is setting the agenda, but what worries me more is the fruits of this will be exploited by the far right, and these fruits are poisonous.”
He also suggested that Mr Trump was damaging the reputation of the US. He said: “Many of the things that are being said and done by Donald Trump cause huge offence and I’m afraid that the reputation of America isn’t as great as it has been in the past because of the president.”
The mayor also repeated his view that it was wrong to give the president a state banquet, adding: ”The red carpet is not an honour that should be bestowed on this president.”
Mr Khan claimed the prime minister’s decision to invite Mr Trump had “backfired” and “has led to a situation where Donald Trump feels he can say and do anything because others will be sycophants.”
“We see the USA as our best friends.” he added. “That means surely that we must have a relationship where we can call each other out.
“We can’t vacate the pitch because we are scared of upsetting Donald Trump.”
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