The crisis in masculinity and the presidential election got hitched in an October surprise unintentionally engineered by Donald Trump. While a vast majority of men—the 2016 election season’s silent majority—reject Mr. Trump’s “locker room” ideas about manhood, many are reluctant to publicly say so. That may be changing.

Mr. Trump’s vile description of how he treats women, and his subsequent disingenuous “apologies” may have encouraged men to speak out as the question of American masculinity took center stage in the campaign. Ironically, the Republican candidate’s attempt to downplay his behavior as locker room banter had the opposite effect, highlighting a culture of sexual assault that men need to play a greater role in uprooting.

I have been part of a movement committed to transforming masculinity for three decades. The kind of manhood I want to pass on to my son and grandsons, and the hopes and dreams I have for my daughters and granddaughter, could not be more different from Mr. Trump’s, a man who is on tape admitting to sexually assaulting women. Ironically, through his vulgar remarks, he may have advanced our cause.

Mr. Trump exhibits virtually every negative trait about manhood the gender justice movement is challenging. Antagonistic. Boastful. Bullying. Conceited. Condescending. Crude. Defensive. Dishonest. Entitled. Inflexible. Juvenile. Lacking in self-awareness. Merciless. Obstinate. Predatory. Privileged. Rapacious. Sexist. Vindictive. All ingredients in a toxic masculinity sludge that men and women in scores of countries around the world are working to eradicate.

One organization, the global MenEngage Alliance and its 650-members in 66 countries, (including Voice Male), is committed to inoculating future generations of boys from the virulent strain of hate and misogyny Mr. Trump is spreading. For decades, activist women have led the way in advancing gender justice; now men interested in equality for their mothers, wives, and daughters must help develop a social vaccine to protect against poisonous masculinity—as well as continuing to develop positive programs to raise healthy boys.

When men hear a man degrade women the way Mr. Trump did on the NBC tape, too often we walk away rather than confront the misogynist head on. Mr. Trump does not represent what most men think manhood is—or, more accurately—what humanness is. All of us were born of mothers; none of us would want them, our daughters, our sisters to ever hear such revolting language, let alone be groped, or worse. I am ashamed to share the same gender with Mr. Trump. And as a father, it is unfathomable to me how he spoke about his daughter. How can any other father or grandfather stand silently by when a presidential candidate describes his daughter as “hot”, saying he’d consider dating her if she weren’t of his own flesh and blood?

I am four years younger than Mr. Trump; like him I am a husband, father, and grandfather. A lot of men believe that if they speak out against Mr. Trump and his ilk—men who contend they can sexually assault women with impunity— that they’ll be bullied, ostracized, labeled “weak.” Is Mr. Trump unwittingly inviting them to speak up?

When it comes to sexual assault, political affiliations are irrelevant. As men we must challenge each other about what we expect of one another—beginning with ourselves. We have to declare unambiguously that denigrating and assaulting women as just “guy talk” or “boys being boys,” is indefensible, inexcusable, unforgivable. Mr. Trump was 59 years old, newly married, and a father of three when he spoke so crudely, not some college frat boy.

By running for president, Mr. Trump gave citizens an unexpected opportunity to begin a serious discussion about contemporary masculinity. Imagine a curriculum developed in classrooms in all 50 states; dialogues on our sports fields; heart to heart talks among faith communities— a nationwide, multigenerational summit about manhood, about boys becoming men. Donald Trump’s ultimate contribution to the 2016 election may turn out to be the teachable moment before us. For the sake of our children and grandchildren, we can ill afford not to begin the conversation. We need not wait until a new president is inaugurated. We can start now.