When will celebrities realize that their political pronouncements often backfire?

The real ideological action is undertaken by the audience, whose members read between the lines of these culture pieces and then scribble in the margins. Breitbart’s two posts on Ms. Dunham have amassed more than 10,000 comments, including this insight: “Lena was an awesome Trump vote recruiter.” Meanwhile, the muted Patriotic Folks piece on Lady Gaga soon migrated to a pro-Trump Facebook page that reaches millions, Make America Great Today, which shared it with a baiting line, “More white women voted for Donald J. Trump than Hillary Clinton.”

Lefty celebrities have long been preaching to the choir, but they are increasingly galvanizing the other side when their chatter is rerouted into an online conservative echo chamber. A study last year by the Bowling Green State University professors David Jackson and Melissa Miller found that celebrity political statements were highly polarizing to a sample set of Ohio voters, and that no celebrity — not Trace Adkins, not Ted Nugent, not even Oprah — was likely to inspire net positive votes for his or her candidate of choice.

These right-wing aggregators make sure that any leftist celebrity’s political reach will be neutralized by a backlash from people who don’t idolize and agree with them. None of that is likely to stop celebrities from using their own soapboxes to promote their politics. But they would be smart to consider how their words will play on other platforms, too.