The king's visit comes amid foreign policy disagreements with the United States.

So annoyed is President Trump about Britain's failure to offer full support for his war against Iran that his administration, according to a memo drafted at the Pentagon, is considering whether to stop supporting British sovereignty over the Falkland Islands, which are also claimed by Argentina. Mr. Trump has directed his anger at the British prime minister, Keir Starmer, who refused to allow British bases to be used in the initial U.S. attack on Iran and who, in the president's words, is "no Winston Churchill." Eager to placate the United States, which is Britain's closest security partner, the government in London is seeking to coordinate international efforts to reopen the Strait of Hormuz, the crucial shipping lane in the Persian Gulf, if a cease-fire with Iran becomes permanent. Yvette Cooper, Britain's foreign secretary, is accompanying the king to the United States and is expected to meet with her counterpart, Secretary of State Marco Rubio. Trans-Atlantic tensions have already forced Britain to suspend plans to give up sovereignty of -- and then lease back -- the Chagos Islands, a remote Indian Ocean archipelago that houses a strategically important British and American military base. Although Mr. Trump at one point supported the British plan, he changed tack after disagreeing with Britain over American ambitions to take control of Greenland, and called the Chagos idea an "act of great stupidity." The British government recently acknowledged that it could not proceed without Washington's backing. Mr. Trump, who has a strong affection for the British monarchy, told The Telegraph newspaper in Britain -- without providing evidence -- that he believed the king "would have taken a very different stand" on the Iran war than Mr. Starmer. But the president has also mocked British warships as "toys," has said the British "don't even have a navy" and has added that their aircraft carriers "didn't work." Such criticism could be uncomfortable for King Charles, who, as monarch, is commander in chief of the British military. He also served in the Royal Navy in his 20s. In January, when Mr. Trump said that the United States had "never needed" its NATO allies in Afghanistan and that alliance troops had "stayed a little back, little off the front lines," the comments infuriated Britain, which lost 457 soldiers during two decades of fighting in Afghanistan. At the time, the British news media reported that Buckingham Palace had relayed the king's concerns over the comments to the White House. Mr. Trump later issued a clarification. Further straining the U.S.-British relationship has been the issue of support for Ukraine in its war against Russia. The king has met with and hosted the Ukrainian president, Volodymyr Zelensky, several times, underscoring Britain's full support for a government in Kyiv that has increasingly been sidelined by the Trump administration. And Mr. Trump's musings about increasing his country's landmass also clash with British interests. The president's threats about taking over Greenland, a self-governing territory of NATO member Denmark, prompted Mr. Starmer to speak out alongside other European leaders. Mr. Trump's suggestion that the United States absorb Canada, a country over which Charles is the sovereign, was followed by a carefully timed visit by the king, with Prime Minister Mark Carney stating: "Canada has a steadfast defender in our sovereign."