Three months after quietly acquiring American clothing brand Everlane for $80 million, Shein — the Chinese fast-fashion company that has fundamentally altered how Americans shop — took the unusual step of inviting U.S. national security regulators to review the completed deal. The move places a single retail transaction at the center of a much larger question: how much control over American consumer culture is Washington prepared to cede to Chinese-owned enterprises. The outcome may define the terms of foreign investment in American retail for years to come.