 -- Standing as a mostly silent presence at the president’s side on his visits to foreign capitals and domestic disaster areas, Melania Trump today stood on her own while addressing a luncheon for spouses of other world leaders at the United Nations.

It was not a speech calculated to challenge anyone in power. This was no Eleanor Roosevelt, a member of the first U.S. delegation to the United Nations, hammering home the need for a Universal Declaration of Human Rights and refusing to rest until it was accomplished.

Nor did this first lady follow in the footsteps of Laura Bush, who used the General Assembly meeting in 2006 to pull together a roundtable on the abuses of the Burmese regime as she spearheaded a lobbying campaign to put Burma on the Security Council agenda.

Instead, Trump spoke as a mother, enlisting other mothers and fathers to “join together as parents caring for children, whether they live in our own families, across the street, across the nation, or across the globe.” In particular, she called on parents to take responsibility for what their children are exposed to on social media.

During the campaign, “cyber-bullying” was Trump’s somewhat surprising (not to mention ironic, given her husband's proclivities on Twitter) answer when she was asked what issue she would focus on if she ended up in the White House. But since then we haven’t heard much from her on that subject or seen any evidence that she is mounting a campaign to address the hurtful and harmful messages that stalk some children.

But today she called on “leaders on social media” to join her “in this fight for the hopes and dreams of our children.”

What Trump might not know is that if she truly makes this a fight, she can win it. Even Bush, who had been a governor’s wife and a president’s daughter-in-law, was astonished when she realized the force her voice could carry.

“I was dense,” she joked in an interview at the end of her two terms in power, but then she learned “when the first lady is interested, all the wheels are greased a lot faster. You really can call attention to things that the general public may not pay that much attention to, or members of Congress may not pay that much attention to.”

If Trump stays on the case, she can grease the wheels against cyber-bullying. She took a step forward today, but now she must be ready to go beyond a comfortable, motherly message and be ready to take on opposition among people who can make a difference. As Lady Bird Johnson told her successors, “the first lady has a podium.” It’s time for Trump to use hers.

Cokie Roberts is a political commentator for ABC News. Opinions expressed in this column do not necessarily reflect the views of ABC News.