Julianne Moore, Jennifer Aniston, and Amy Schumer were among a group of Hollywood celebrities who joined President Obama in a post-San Bernardino gun control video ad produced by Everytown for Gun Safety. The three actresses were joined by other celebrities-including Kevin Bacon, Michael J. Fox, Sofia Vergara, Sarah Silverman, Ty Burrell, and Nick Offerman-each of whom take turns looking into the camera to say, "We can end gun violence." No one explains how to end it, but they take turns saying the words and, at times, repeat the sentence over and over together.Obama takes time to say, "When we come...