If April DeBoer were a man, or James Obergefell a woman, or Valeria Tanco a man, or Greg Bourke a woman, then state law would readily give them the relief they seek. But because the state laws challenged in these cases provide that only a man can marry a woman and only a woman can marry a man—or that existing marriages will be denied recognition if they do not fit this description—April and James and Valeria and Greg are being discriminated against on the basis of their gender. Such sex-based classifications constitute sex discrimination. Accordingly, they must be subjected to intermediate scrutiny. The justifications the state offers not only fail to satisfy such scrutiny. They are themselves based on the precise invidious sex stereotypes that intermediate scrutiny seeks to uncover....