Not among them: Sen. Bernie Sanders of Vermont. The runner-up in the Democratic presidential primaries was in Burlington, Vt., ahead of a simulcast speech to supporters today. (He is not expected to concede.) He'd been in Washington the night before the filibuster began, for the Democratic luncheon and a meeting with Hillary Clinton, but he was not able to return to the city.

"It just didn't work yesterday," said Sanders spokesman Michael Briggs. "We're keeping an eye on votes next week."

Sanders, who opposed the Brady Bill that expanded background checks and waiting periods, has since come into sync with the Democratic caucus. "The idea that weapons designed to do one thing — kill people by the dozens — should be sold and distributed in our country is absurd," he said Tuesday. On Wednesday, he tweeted in support of the filibuster.

Hillary Clinton did roughly the same thing.

But Sanders's physical absence was noticed on social media, and a bit of a departure from his approach to the Senate. In 2010, the senator waged a one-man filibuster against a compromise that allowed most of the Bush-era tax cuts to continue. It did not delay the vote on that compromise, but it captured liberal attention and raised Sanders's profile, with the text of the speech soon collected into a book.