WASHINGTON — All the atmospherics about today’s extraordinary oral argument on campaign finance reform at the U.S. Supreme Court scream “landmark!” or, at least, “very big deal!”

The details are familiar by now. The uniqueness of a September sitting, when the court usually starts up in October. The first time new Justice Sonia Sotomayor will be on the bench at argument, bumping the other associate justices into new seats for the first time in three years. The debut also of Solicitor General Elena Kagan — will she wear the swallowtail morning coat or not? — matched up with other titans of the Supreme Court bar. Former SG Seth Waxman will argue on her side, and former SG Theodore Olson against her.