Donald Trump has often touted his experience as a negotiator, a skill he has said would be essential as president.
But his response on Monday to British leaders' criticism of his proposed ban on Muslims entering the United States has raised a second question – how would a President Trump sustain the long-running "special relationship" between the two nations?
"It looks like we're not going to have a good relationship," Mr. Trump said in an interview on ITV's "Good Morning Britain" broadcast on Monday, in response to a question about Mr. Cameron, who has called the proposal "stupid, divisive and wrong."
"Who knows, I hope to have a good relationship with him, but he's not willing to address the problem either," he said. A spokesman for Cameron told the station that the prime minister's stance on the ban had not changed.
"No. 1, I'm not stupid, OK?" the presumptive Republican nominee told the station, adding that he considers himself "a unifier."
But he also increased his war of words with Sadiq Khan, London's mayor, who has called Trump "ignorant" and rejected his offer to be an "exception" to the ban on Muslims coming to the US.
In response, Trump called on Mr. Khan, who became London's first Muslim mayor earlier this month, to take an IQ test, saying his statements were "very rude."
The spat was closely watched in Britain, which has long touted its close relationship with the US. Khan's election victory came following what one former minister called an "appalling dog whistle campaign" launched by Conservative Zac Goldsmith and supported by Cameron.
But criticisms of Trump's proposed ban appear to have united prominent members of both parties, with outgoing mayor Boris Johnson, a Conservative and likely candidate to be Cameron's replacement as prime minister, also saying Trump's "stupefying ignorance" made him "unfit" to be president.
The Financial Times' Sebastian Payne notes that the presumptive GOP nominee could face a hostile reception if he makes a trip to Britain to nurture a relationship between the two countries:
These trips can be a mixed blessing. Scott Walker, Republican governor and potential presidential candidate, had a difficult time when he visited London last year. Mitt Romney’s visit in 2012 was widely considered to be a disaster after he offended most of the country by questioning whether it was ready for the Olympic Games.…The best [Trump] could hope for would be a chat with Nigel Farage, the leader of the UK Independence party, who said he would back him in a straight fight with Hillary Clinton.
In the interview on Monday, Trump attempted to navigate what might turn out to be a contentious relationship with Cameron. He has also said the proposed ban was "just a suggestion."
"Britain's been a great ally. With me, they'll always be treated fantastically," he said in response to a question about the country's upcoming vote on whether to leave the European Union. "I am going to treat everybody fairly but it wouldn't make any difference to me whether they were in the EU or not."
When asked about Khan, he appeared to take umbrage, first saying he didn't care about the London mayor, then adding "I think they were very rude statements and, frankly, tell him I will remember those statements. They are very nasty statements."
The mayor responded by doubling down on his own criticisms and declining the presumptive Republican nominee's challenge to take an IQ test, saying "ignorance is not the same thing as lack of intelligence," CNN reports.
Trump's comments point to wider repercussions for the "special relationship," argues The Telegraph's John McTernan:
There is no doubt that Trump is not just a threat to the special relationship – he would be the end of it. It would not just be the fractious personal relationship – there is no conceivable British prime minister who would be able to fake respect for Trump's intellect and strategic insight. It is, fundamentally, what a Trump victory would mean: a triumph for nativism and isolationism. He means it when he says the US pays too much to defend the rest of the free world and even though the UK bears the cost of the deterrent we would not be immune.
With the Muslim population in England and Wales nearly doubling in 10 years, and 73 percent identifying themselves as British, according to a survey by the Muslim Council of Britain, Trump's proposals could have a particular impact.
"So whilst it may be great that he's made an exception for me, it's not about me," Khan told the BBC last week. "It's about my friends, family and others from all around the world who want to go to America, and my concern is he's playing into the hands of extremists who say it's not compatible to be Western and to be a mainstream Muslim."