A day after Vice President Kamala Harris announced that she intended to seek the Democratic presidential nomination, more than 40,000 Black men from across the country convened on a virtual fund-raising call to discuss what the moment required of them.

For four hours, one Black man after another — prominent politicians, activists, entertainers — laid out the challenges ahead for Ms. Harris, including the racist and sexist attacks they expected from her opponents. In pledging their support, many offered emotional testimonies about the personal relationships they have built with her.

But it was not long before the men confronted the elephant in the room.

“Sometimes as Black men we get confused as to what strength is, and sometimes we think that standing behind a Black woman as a leader does not display strength as Black men,” said Kwame Raoul, the attorney general of Illinois. “I’m here to tell you all tonight that it does the opposite of that, it displays strength.”

Mr. Raoul then drove home his point. “I’m standing behind a Black woman to be president of the United States, and it doesn’t make me any less of a Black man,” he said. “I’m asking all of you all to do the same.”

The call, one in a series the Harris campaign has held in recent weeks with Black women, white women and white “dudes,” was a rallying cry to a part of a crucial Democratic constituency seen as skeptical of Ms. Harris.

While Black men have been reliable voters for Democrats for decades, Mr. Raoul was touching on an uncomfortable truth: A small but significant slice of Black men have historically been hesitant to support Black women seeking the highest positions of power. The numbers are on the margins but could be crucial to carrying Ms. Harris to victory in November.