New Delhi, Nov. 4 -- Featuring one of the most diverse slates of both Democratic and Republican candidates in recent years, this midterm election has set up a possible wave of historic leadership firsts across the country.

Voters on Tuesday night elected the first openly gay male U.S. senator. They could still propel into office the first Native American female governor and Native women senators, the first Black female governor and the first Muslim U.S. senator, among other milestones. Most are Democrats, but the GOP could also break ground.

While some of these candidates have avoided focusing on the inherent historic value of their race, gender, religion or sexual orientation, some voters' rights advocates are celebrating how the elect...