The guardian of the special relationship—the historical but possibly mythical bond between the United States and the United Kingdom—is a short woman with discerning blue eyes and a penchant for glittering headbands.The role of an ambassador has always been strange. They’re expected to be fun—to flit around comfortably at galas and cocktail parties, charming guests and making inroads with important people while waiters weave around with platters of deviled eggs. Still, British Ambassador Karen Pierce’s real duty is to lobby for her country and offer advice on delicate matters during heated international moments. And the job of an ambassador—even one representing a close ally—has become far more complex because of the strident partisanship that has taken hold in D.C.Part of Pierce’s mission recently has been to represent the British government’s firmly pro-Ukraine position on providing military aid—even when the Biden administration’s matching desire became mired in Congress because of protests by a Trump-aligned faction of House Republicans.[Elaine Godfrey: Trump’s VP search is different this time]Pierce had not only lobbied hard on Capitol Hill ahead of last week’s long-awaited congressional vote on aid; she’d also traveled with Britain’s foreign secretary, David Cameron, to Mar-a-Lago to try to get buy-in from Donald Trump. (She has been tight-lipped about their meeting, and was certainly claiming no credit, but the former president’s toned-down opposition to the bill probably did help the package pass—even though more Republican lawmakers voted against it than for it.)In an era when populist politics and rising nationalism are challenging the institutions of the international liberal order, diplomacy can seem like a quaint relic of bygone etiquette.The more public side of an ambassador’s job seems much easier. Over the past three years, Pierce has become well known for throwing lively and well-attended Pimms-fueled bashes, especially in the D.C. social season surrounding the annual White House Correspondents’ Dinner. Underneath the surface frippery, though, Pierce is a serious operator. The true art of her diplomacy is the very English thing of working hard to make it all look totally effortless.One evening last week, I watched Pierce at work. During a party two days before the WHCD, she buzzed around the lush green garden of her Washington residence, chatting with various politicos.The 64-year-old Pierce grew up in northwest England and has worked for the U.K.’s Foreign Office for 43 years. She’s held positions in Japan, in Ukraine, and in the Balkans during the conflicts in former Yugoslavia. For a year, she lived in Kabul as Britain’s ambassador to Afghanistan, and she represented the U.K. at the United Nations for three years. Although she was made a dame in 2018, Pierce’s working-class background makes her a relative outsider in the foreign service, which is otherwise a bastion of the upper-class elite. Being Britain’s first female ambassador to the U.S. does too. She leans into it.The day I saw her, she was wearing a vivid chartreuse dress and black tights, with her feet tucked daintily into a pair of black-and-white kitten heels. Despite being shorter than everyone else at the party, she still commanded the attention of all the people in her vicinity. Pierce has worn tangerine suits to state events, and baby-pink silk dresses with huge round sunglasses. Once, to attend a UN summit, she wrapped herself in what looked like a maroon feather boa. Such displays aren’t just a sartorial choice; they’re a strategy.“When you’re an ambassador, you want people to remember you,” she told me. So I made note of her leaf-patterned sheath dress, shiny blue blazer, and cheetah-print headband. About that feather boa; it wasn’t one. “It was a fur, but it was fake,” Pierce insisted. “Though the Russians tried to say it was an exotic fur.” She rolled her eyes. “The Russians will go for anything. They really have no scruples whatsoever.”[Read: What a former U.S. ambassador to Russia learned from Condoleezza Rice]The wall behind the desk in Pierce’s office, a cheerful, sunlit room in an otherwise sterile building, is covered in magnets collected from around the world (“The tackier the better,” she told The Washington Post). Orchids decorate the tables.Entertaining is part of the job. But don’t call them parties: “We would call them receptions, because we treat them as work events,” she chided me. In the days surrounding the WHCD on April 27, Pierce hosted an embassy reception that provided not only a selection of assorted British pasties, but a cigar room and Scotch bar as well. She also made appearances at half a dozen events put on by various Washington bigwigs and media outlets, and emceed a Sunday brunch in the embassy garden. Pierce’s drink of choice? “I like lots and lots of cocktails, but the more pink they are, the better, I’m afraid.”Pierce’s first job in D.C. was as private secretary to the then-ambassador. She arrived in 1992 with her husband, former U.K. Treasury Secretary Charles Roxburgh, and her first of two children, an infant at the time. “The fact that politics is in the air is just—and also the fact that you’re in the capital of the leading nation in the world—I get a real buzz out of that,” she said.In 1995, Pierce watched as Newt Gingrich became speaker of the House, and American politics grew more polarized. When she came back to serve as ambassador in March 2020, she saw that trend intensify, culminating in the Capitol riot on January 6, 2021. “I watch all of these developments, and we spend a lot of time evaluating them and finding historical context for them,” she told me.But Pierce wasn’t particularly eager to discuss current politics—or the ex- and possibly future president who has sent that polarization into overdrive. Her caution made sense: Pierce’s predecessor, Kim Darroch, resigned from his position after leaks revealed that he’d criticized the Trump administration as “inept and insecure.” When I asked her about the former Conservative Prime Minister Liz Truss, whose time in office famously lasted only about as long as a head of lettuce stayed fresh, and who has recently cozied up to the former Trump strategist Steve Bannon, Pierce’s expression was steely. “She’s a private individual, and she’s welcome to pursue her politics,” she said. “It’s not where the British government is.”[Read: America’s Trumpiest ambassador]The day after we met in her embassy office, Pierce showed up early at the Hilton Hotel, in a rich-blue gown and a pair of cascading diamond earrings, greeting as many people as possible before the Correspondents’ Dinner officially began. This year’s dinner was probably Pierce’s last spring soirée; a new British ambassador is expected to replace her by the end of 2024.Leaving will be hard, Pierce said during a Politico podcast taping—“I’ll have to be dragged out of [here] by my fingernails”—not least because this is an election year. A return to the Oval Office for the resident of Mar-a-Lago could mean a challenging new dynamic between the U.S. and the U.K. Pierce joked about being reluctant to leave America, but her concern about a possible end of aid to Ukraine seemed obvious.That aside, her domestic assessment was surprisingly rosy—or at least highly diplomatic. “I personally do not worry about America,” she told me. “I have a lot of faith in American democracy and in Americans, and I think you have very strong institutions.” Pierce’s faith in what an ambassador to America can achieve seemed unshaken, even amid the capital’s current dysfunction. She didn’t hesitate to assert that confidence when I asked her advice for her soon-to-be-announced successor: “Make the weather.”