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Colorful U.K. Foreign Secretary Boris Johnson is pushing back on anti-Trump and anti-U.S. rhetoric in his country, talking up ties between the two nations and slamming “puffed up pompous” Trump-bashers.

On Monday, he warmly embraced Secretary of State Rex Tillerson in London and called the U.S.-U.K. relationship “absolutely fundamental” to both diplomacy and the economy.

“There is no other economic relationship like it and we’re very glad to welcome you here today, Rex,” Johnson, who has frequently been tipped as a future prime minister, said.

Johnson, a member of the ruling Conservative Party, has been particularly defiant in the face of anti-Trump rhetoric that has, so far, succeeded in preventing Trump from visiting the country.

Both hard-left Labour Party leader Jeremy Corbyn and London Mayor Sadiq Khan have repeatedly called for Trump not to be invited to the U.K. and have warned of mass protests if he did.

Khan celebrated after Trump announced this month he would not be visiting the U.K. on a planned visit, bragging that Trump had “got the message.”

Johnson quickly responded and promised that the U.S.-U.K. relationship would not be harmed by a “puffed up pompous popinjay in City Hall.”

This week he followed those remarks up with an op-ed in The Sunday Telegraph, saying that Trump, "our closest ally," should be welcomed to the U.K.

“[Trump] was voted into office by millions of Americans – not bad people, but on the whole good and kindly people with whom we are connected by old ties of blood and friendship and with whom we have the single most extraordinary economic relationship,” he said.

In response to Corbyn’s claim that the U.S.-U.K. relationship is not the most important one, Johnson said the remark “betrays not only his anti-Americanism but also his ignorance of this country’s economic interests.”

“Our partnership with America transcends economics, or foreign policy, or the invisible skein of shared intelligence that is so vital for our collective security. It is about shared values – and one would have thought those values, of freedom and democracy, were shared by Labour,” he wrote.

In the piece, he went on to attack the left for daring to “rant and fume about ‘Trump’s America’” while keeping a “contemptible silence about the real abuses of human rights in left-wing Venezuela.”

“Chuck it, Corbyn,” he added.

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Labour Party leader Jeremy Corbyn has been a vocal critic of President Trump. (Reuters)

Johnson, who was born in New York City and until 2016 held dual citizenship, also went rogue Monday by appearing to contradict the U.K. government’s frosty reception toward the move of the U.S. Embassy in Israel to Jerusalem. While Prime Minister Theresa May's office had called the move “unhelpful,” Johnson instead spoke of a “moment of opportunity” for peace in the region.

“A process that has been stalled for years, if not decades, could see some progress. And everybody is very interested to see what the United States comes up with,” he said, although he added that he hoped to see a “symmetrical movement in the other direction” as well.

The remarks sparked criticism from left-wing MPs in Parliament, with Chris Bryant calling it a “complete capitulation and abandonment of a two-state solution."

“Boris Johnson seems to be making policy up on the hoof, which is only going to make it harder to achieve a two-state solution,” Bryant, a member of the Foreign Affairs Select Committee, told The Independent.

Never one to back down from a fight (last year he appeared to nearly push a Labour MP to the floor during a TV debate about membership of the E.U. customs union), Johnson is unlikely to be cowed by such criticism. In 2015, he caused a diplomatic hubbub on a trip to Israel as mayor of London when he mocked those calling for a boycott of the country as “corduroy-jacketed, snaggle-toothed, lefty academics.”

When he was named foreign secretary in 2016, remarks resurfaced from 2007 in which the former journalist had written an article describing Hillary Clinton as having “dyed blonde hair and pouty lips, and a steely blue stare, like a sadistic nurse in a mental hospital.” Diplomatic difficulties were averted when Clinton went on to lose her bid for the presidency.

Shortly before becoming Britain's top diplomat, he caused an uproar when he used an April 2016 column to speculate about then-President Barack Obama's decision to remove a bust of Winston Churchill from the Oval Office.

"Some said [the move] was a snub to Britain," Johnson wrote. "Some said it was a symbol of the part-Kenyan President’s ancestral dislike of the British empire – of which Churchill had been such a fervent defender."

Not only is Johnson a key foreign policy player on the world stage, he has repeatedly been named as a top prospect for 10 Downing Street should current Prime Minister May step down.

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Johnson was born in New York City and held dual citizenship until 2016. (Reuters)

As a key campaigner for Brexit in 2016, he was widely seen as a likely successor to then-Prime Minister David Cameron, who stood down after the referendum. But a decision by key ally Michael Gove to run torpedoed Johnson's chances, and he abandoned his bid.

Yet Johnson’s moves, particularly his frequent distancing of himself from official policy positions of Number 10, has led to speculation that he is lining himself up to replace May -- whose position has been significantly weakened after disappointing election results for the Conservative Party last year.

This week, Johnson reportedly angered members of his own party and was admonished by fellow Cabinet members after he was accused of briefing reporters that money saved from departing the European Union -- the so-called “Brexit dividend” -- should be spent on the country’s struggling National Health System.

Chancellor of the Exchequer Philip Hammond responded to questions about Johnson’s claims by tersely reminding reporters that neither spending nor the NHS were in Johnson’s brief: "Mr Johnson is the foreign secretary," he said.

Another senior Tory MP was less polite when speaking to the Times of London: “Boris is a w---er. If anyone asks me about Boris or Michael [Gove], I just say they are journalists who are only after the headline.”