That agenda and Johnson’s recent efforts to cozy up to Trump should make for a chummy start after the stilted relationship Trump had with Johnson’s predecessor and recent political antagonist, Theresa May.

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“There will be good chemistry between them, and President Trump will enjoy Boris’ company and humor,” said Andrew Mitchell, a former Conservative Party lawmaker and Cabinet minister. “The contrast with the president’s relationship with Mrs. May could not be greater. This will be good for Britain and also for America: Trump and Boris may turn out to be good for each other.”

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But how long that friendliness lasts probably depends on whether Johnson can deliver on Brexit, and whether Trump can overlook continuing disagreements between London and Washington on key issues, including Iran, Russia, climate change and the Israeli-Palestinian conflict.

“Good man. He’s tough and he’s smart,” Trump said Tuesday, shortly after Johnson’s election as leader of the Conservative Party, during remarks to an audience of young supporters. “They say the British Trump. They say that’s a good thing. They like me over there. That’s what they wanted. He’ll get it done. Boris is good. He’ll get it done.”

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Trump is not popular in Britain — a July 2018 Ipsos Mori survey found 19 percent had a favorable opinion of Trump, while 68 percent were unfavorable — and his state visit in June was met with street protests.

This distaste for the U.S. president will probably prove to be a major challenge for Johnson, who, while seeking to take advantage of his good relationship with Trump, will have to ensure he is not seen as following his lead too often.

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“Clearly there’s going to be a close personal relationship between the two, but if it plays out the wrong way for Boris in the U.K., it could be more of a problem than a help,” said Alan Duncan, who quit as a Foreign Office minister on Monday because he was not prepared to serve under Johnson.

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Relations between the United States and Britain — for decades the foremost Western alliance — have been touchy throughout Trump’s tenure despite May’s attempts to appease him. Ties are at a low point after the resignation this month of British Ambassador Kim Darroch over his leaked assessment that Trump’s administration is “inept” and adrift.

Trump called Darroch a “pompous fool” upon publication of the ambassador’s internal memos, and he said the White House would no longer work with the veteran British diplomat.

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Johnson, a former British foreign secretary who was the ambassador’s boss for two years, declined to back Darroch. That decision in the closing weeks of the Conservative Party leadership contest was seen as an overture to Trump. It was also condemned by MPs across the political spectrum.

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Questioned on Trump’s controversial “go back” tweets about four nonwhite congresswomen, Johnson said they were “completely unacceptable” but declined to say whether he believed they were racist.

Having once accused Trump — then a presidential candidate — of demonstrating “a quite stupefying ignorance that makes him, frankly, unfit to hold the office of president of the United States,” Johnson has since deployed a combination of flattery and charm to build a close alliance.

It worked.

Last week, as Johnson neared an expected victory, Trump cheered him on.

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“I like Boris Johnson. I always have,” Trump said on July 19. “He’s a different kind of a guy. But they say I’m a different kind of a guy, too. We get along well. I think we’ll have a very good relationship.”

Trump had bluntly criticized May’s approach as too slow and cautious, and appears at ease with Johnson’s insistence that Britain will leave in October with or without a step-by-step plan for managing the departure. Economists have warned that a “no-deal Brexit” could be disastrous.

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It remains to be seen whether Johnson can remain in the famously fickle and temperamental Trump’s good graces.

May tried to placate Trump, with little to show for it, said Amanda Sloat, an expert on Brexit and European politics at the Brookings Institution.

“He’s coming into the government not wanting to upset Trump,” Sloat said. “We’ve all been watching Trump long enough where we know he doesn’t reciprocate. He was quick to throw Theresa May under the bus.”

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Johnson may also have to be wary of Trump’s strong relationship with Brexit architect Nigel Farage if he finds himself having to make compromises as part of managing Britain’s departure from the European Union. Farage is likely to be critical of any such moves and unafraid to communicate them to Trump.

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On Tuesday, Farage attended the Turning Point USA conference in Washington where Trump spoke — a point he made sure was well known.

“Backstage at the @TPUSA conference in Washington. About to hear @realDonaldTrump speak, huge youth enthusiasm here,” he tweeted.

In the past, Trump has suggested Farage would make a good British ambassador in Washington.

The areas of disagreement between the United States and Britain will not change overnight with Johnson’s ascendancy, said a British official speaking on condition of anonymity to discuss the two men’s future partnership.

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A Johnson government is not likely to begin aping Trump’s antagonism of NATO, flattery of Russian President Vladimir Putin or rigid opposition to Chinese tech giant Huawei, a builder of 5G infrastructure that the Trump administration is pressuring Britain to swear off.

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It is also not expected to change its backing of the Iran nuclear deal that Trump pulled out of last year. Britain has resisted what it and other European countries see as Trump’s subsequent efforts to kill off the deal altogether.

It is possible, however, that Johnson could seek to curry favor with Trump by taking a harder position on Iran, the official said, noting that Trump’s national security adviser, John Bolton, has been pressuring the United Kingdom to act more aggressively against the Middle Eastern country as London and Tehran seize each other’s vessels and tensions flare in the strategic Strait of Hormuz.

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Earlier this month, Britain seized an Iranian oil tanker near Gibraltar, saying it was taking embargoed oil to Syria. Then last week, Iran captured a British-flagged tanker, the Stena Impero, and is holding the vessel and its 23 crew members.

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Secretary of State Mike Pompeo has said Britain is responsible for the safe passage of its own ships, and the British are negotiating establishing a “marine protection” coalition with other European countries. Iran’s foreign minister, Mohammad Javad Zarif, in congratulating Johnson on his win, also warned in a tweet that “these are our waters and we will protect them.”

May had also distanced herself from Trump over his recognition of Jerusalem as the Israeli capital. On Tuesday, just after Johnson’s victory, the top British diplomat at the United Nations reiterated her government’s commitment to the goal of an independent Palestinian state. Trump’s Middle East peace plan is expected to fall short of that ideal.

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Iain Duncan Smith, former leader of the Conservative party and chair of Johnson’s leadership campaign, predicted that the two leaders can work out any differences.

“I believe their relationship will be a strong one,” he said. “Boris I believe will be able to have very straight conversations with him as I believe there is mutual respect. Both believe that when the U.K. and the USA are together the world is a safer place, that’s a vital starting point.”