Seventy-five years ago, the United States and Britain joined with other Allied nations to invade Normandy on D-Day, beginning the end of the Nazi occupation of Europe. Since then, the two countries have been close partners, fighting wars alongside each other—including two full-scale invasions in the past 20 years—and sharing intelligence at the highest levels.

But just how enduring is this partnership—and is it strong enough to withstand another visit from Donald Trump, one of the most unpopular foreign leaders in Britain?

President Trump’s June 3–5 state visit to the United Kingdom comes at a period of immense uncertainty for Britain, in terms of both when—or if—it will leave the European Union and who will lead the country when it does. It also comes at a low point in U.S.-U.K. relations.

Both sides continue to work together on defense, and a senior U.S. administration official, speaking to reporters on the condition of anonymity, insisted that Trump’s visit underscored that “the relationship isn’t just based on personalities. It’s based on the long-shared service and shared sacrifice.”

Still, the “special relationship” between the two countries has seen better days. In 2019, they are divided over how to deal with Iran (Washington has withdrawn from the nuclear deal with Tehran that London, along with its European partners, has struggled to keep alive), and they are split on Huawei and the implications of Britain’s decision to allow the Chinese company to build part of its 5G network. They have even sparred over Britain’s domestic politics: Whereas a majority of British lawmakers oppose a scenario in which their country would leave the EU without a withdrawal agreement, Trump appears to have all but encouraged a no-deal Brexit.

The point of Trump’s state visit, seemingly, is to quell those divisions—if not in practice, then at least aspirationally.

The last time Trump visited London, the climate was, well, tense. Mass protests were organized. A large yellow blimp depicting the U.S. president as a baby was deployed. Ceremonial faux pas were committed. Trump even managed to insult Prime Minister Theresa May by openly criticizing her strategy to deliver Brexit (comments for which he later apologized). As my colleague Rachel Donadio reported at the time, the whole affair proved to be “less a triumphant celebration of the ‘special relationship’ between two long-standing allies and more an exercise in damage control.”

That exercise in damage control is likely to be on display this time around too. In interviews with British newspapers ahead of his trip, Trump once again criticized May’s handling of Brexit; said that Nigel Farage, the leading Brexiteer, should be put in charge of negotiations with the EU; added that he thought Boris Johnson would be “excellent” as the next leader of the Conservative Party and, consequently, as British prime minister; and appeared to insult Meghan Markle, the former American actress who is married to Prince Harry.

Despite the clear strains, those who work to maintain the U.K.-U.S. relationship say it is fundamentally intact. Last month Michael Garrett, the commanding general of the U.S. Army Forces Command, highlighted the interoperability of the two countries’ armed forces and called the bonds of defense cooperation “unshakable.” Woody Johnson, the U.S. ambassador to the U.K., has dubbed the defense partnership “the envy of the world.”

Indeed, Britain has one of the highest numbers of deployed soldiers in NATO and, unlike most of the military alliance’s members, meets the 2 percent defense-spending threshold, a persistent demand of Trump’s. British Foreign Secretary Jeremy Hunt, one of a dozen potential successors to May, has called on the government to increase that figure over the next decade. But Britain’s military might isn’t what it used to be. Budget cuts have sparked warnings from former military officials that the country’s status as a credible power could be “at risk.” Meanwhile, it’s France, not Britain, that has emerged in recent years as the U.S.’s key NATO ally in Europe.

U.S. officials dismiss any suggestion that the U.K.-U.S. alliance has weakened. “We do more together than any two countries in the world,” Eric Pahon, a spokesman for the Defense Department, told The Atlantic, adding: “Our special relationship is not a historic artifact, but a current reality and strength for both of us.”

Just because the alliance is strong, however, doesn’t mean it can’t be tested. Iran is one issue where further posturing from the U.S. could spark a potential, if unintended, military escalation—one that would force Washington’s allies to make some difficult decisions. A more aggressive stance “could be something that creates disagreement on the defense side,” Amanda Sloat, a former State Department official who is now with the Brookings Institution, told The Atlantic.

For Britain, such foreign-policy concerns have taken a back seat to the country’s single most glaring issue: Brexit. With five months left before its next Brexit deadline—at which point the U.K. is expected to exit the EU—it’s still unclear how, or even if, the country will leave the bloc, let alone who will be prime minister when it does. A strong relationship with its trusted ally, as well as its most promising future trade partner, will be vital.

“The U.S., under this administration, appears to be willing to directly link trade politics to national-security concerns,” Leslie Vinjamuri, the head of the U.S. and the Americas Program at the London-based Chatham House, told The Atlantic, noting that Trump could use their disagreements on issues such as Iran and Huawei to seek concessions. “Trying to engage as a serious partner while being handicapped is not an easy thing to do—especially in a context when there’s a lot of pressure coming down on you from the United States to take a certain set of positions.”

In addition to all the pomp and circumstance that a formal state visit entails (such as a ceremonial welcome outside Buckingham Palace and a state banquet hosted by Queen Elizabeth II), Trump’s stay will include a news conference with May, as well as meetings with members of the royal family. The visit will conclude Wednesday with an event commemorating the 75th anniversary of D-Day in the southern English city of Portsmouth, a powerful reminder of how both countries have stood by each other through the most difficult times.

“This is why we’re having the state visit,” Vinjamuri said. “It’s not because the queen loves Donald Trump. It’s because the head of state of the United Kingdom recognizes the deep significance [of the transatlantic relationship] … to try and keep it going at a very difficult moment.”

Kathy Gilsinan in Washington, D.C., contributed reporting.