Donald Trump thinks Hillary Clinton is playing “the women’s card.” But evidence suggests that if anything is making gender a potent issue in this campaign, it’s Mr. Trump’s words, not Mrs. Clinton’s.

How do we know? New data on the emotional engagement and effectiveness of different campaign messages suggests that it’s far easier to drive down support for Mr. Trump by highlighting the derogatory things he has said about women than it is to drive up support for Mrs. Clinton by talking about her as a strong woman.

Over the last few weeks and every week between now and Election Day, John Geer, a Vanderbilt University political scientist, and I are running SpotCheck, an experiment testing the effectiveness of campaign ads. Each week, we randomly assign 1,000 people to see one of two campaign ads, both ads or an ad for an insurance company that is not political. Using tools provided by YouGov, G2 Analytics and SageEngage, people rate the ads in real time, revealing the moments they like and dislike. You can see the results from the weekly experiments here.

A few weeks ago, we tested two ads about gender. After Mr. Trump made comments suggesting women should be punished if they got an illegal abortion, we tested the same two ads again. The results picked up a difference in the importance of gender — both ads gained in effectiveness after his comments, though it’s also true that one was far more effective than the other in both periods tested.