SEOUL—Imagine a contretemps of near-crisis proportions involving one of America's closest allies, and no U.S. ambassador is around to ease the pain, to offer soothing words, to grease the way for high-level summitry and exchange backstage confidences.

That's how it's been in Seoul for more than a year now since the departure of the last American ambassador, Mark Lippert, a veteran of Barack Obama's White House staff, a gregarious figure, accessible and outspoken. While North Korea's leader Kim Jong Un has been ordering missile shots and South Korea has undergone a cataclysmic domestic leadership transition, the U.S. embassy here has plodded on with no one to enunciate U.S. policy definitively through the first year of Donald Trump's tumultuous presidency.

"It's puzzling," said a Korean official, musing over the absence of an ambassadorial face. "Maybe we're not that important."

“No, no!” diplomats at the American embassy keep saying as they sit in their its box-like structure, hastily built in the early years after the Korean War, across a broad avenue from the foreign ministry. “No problem, everything is fine.”