There were cherry blossoms. There were silk and glass butterflies. There were toasts. There was an entree inspired by a California roll and a performance by Paul Simon. But before that, there was the photo op, and the fashion.

On Wednesday evening, as the Bidens hosted Prime Minister Fumio Kishida of Japan and his wife, Yuko Kishida, at the fifth state dinner of the Biden administration, Dr. Jill Biden, wearing an evening dress from Oscar de la Renta, stood with her husband to greet their guests of honor at the North Portico.

Designed by Fernando Garcia and Laura Kim, the dress flowed in a watery fade from sapphire blue to light silver and was covered in hand-embroidered floral geometric beading.

Why did it matter? It wasn’t as symbolically obvious as the cherry blossom print gown worn by Naomi Biden or Hillary Clinton’s heavy silk caftan, but in opting for de la Renta, the first lady was not simply supporting an American company that represents the melting pot myth of the country. She was connecting to a longstanding relationship: Oscar de la Renta has dressed almost every first lady since Jackie Kennedy; Dr. Biden first wore the label for her inaugural state dinner in 2022.

On a night meant to underscore another powerful relationship — that of the United States and Japan — and reaffirm the strength of that mutual commitment through political stagecraft, the label was an apt choice.

And it suggested that Dr. Biden, who has not always seemed interested in the game of fashion diplomacy, is gearing up with every means at her disposal to help amplify her husband’s message, not just as president but as the Democratic presidential nominee as he faces off against an opponent who revels in the reality TV nature of politics — complete with costumes.