According to the NBC News/Marist poll, conducted on October 23-27 among 910 adult people, 44 percent of voters have already cast their ballots during early voting. Fifty-one percent of early voters supported Sinema, while 47 percent voted in favor of McSally.
Sinema, 42, is most popular among people with a Latin American background, independent voters and women, while McSally, 52, is mostly supported by white voters and men.
Republicans currently hold a 51-49 majority in the Senate, meaning that Sinema's win could be one that help shift control of the upper house to the Democrats. Arizona has had two Republican senators since the 1980s.