A network of Democratic donors and operatives are organizing an ambitious effort to elect African-American candidates for governor and Congress in 2018 — politicians who have often been overlooked by the party’s predominantly white leadership in past years.

They see the 2018 elections as a crucial opportunity to elect a wave of black candidates, especially to governorships, where only two African-Americans have been elected in U.S. history but a half-dozen prominent hopefuls are running this year. Many organizers also see running strong black candidates as a key way to inspire higher African-American voter turnout that will boost the whole Democratic Party in November.

But their efforts are also motivated by weariness, some said, of watching local and national Democratic groups — and the largely white donors who fund political campaigns — pass over promising African-American politicians before, even during the Obama era, when many expected the election of the nation’s first black president to usher in more black officials in his wake.