WASHINGTON — There seemed little question after the argument in an important campaign finance case at the Supreme Court on Wednesday that the makers of a slashing political documentary about Hillary Rodham Clinton were poised to win. The open issue was just how broad that victory would be.

The argument was extraordinary in its timing, length and participants. It took place during the court’s summer break, almost a month before the start of the new term in October; lasted more than 90 minutes instead of the usual hour; and featured the Supreme Court debuts of Justice Sonia Sotomayor and the solicitor general, Elena Kagan.

It was, moreover, a rare re-argument. When the case was first heard in March, it centered on whether the restrictions on corporate spending in the 2002 McCain-Feingold campaign finance law applied to the documentary “Hillary: The Movie,” which was produced by a nonprofit advocacy corporation called Citizens United. In the request for re-argument, the court raised the much broader question of whether it should sweep away restrictions on political speech by corporations.

On Wednesday, Ms. Kagan all but said that a loss for the government would be acceptable, so long as it was on narrow grounds.