Mr. Brooks is expected to leave the civil rights organization at the end of June when his contract expires. The group will begin searching for a new leader while Leon W. Russell, chairman of the group’s board, and Derrick Johnson, the vice chairman, head up day to day operations.

Both Mr. Russell and Mr. Johnson said the group needed to change to more effectively push back against Mr. Trump’s stances on issues including voting rights laws, public education, environmental policy and the criminal justice system. The group, which has been eclipsed in many ways by the more youthful Black Lives Matter movement and the broader “resistance” to Mr. Trump, is launching a national listening tour of cities across the nation to get ideas about how it can remain relevant.

“We have to work together with other folks, young folks, old folks, in-between folks to ensure that we stop the kind of cynicism, the kind of relapse to a bad old situation that Trump represents,” Mr. Russell said.