CHARLOTTE, N.C.—Democrats watching the must-win state of North Carolina are keeping a close eye on African American turnout in the state, which dropped by 9 points in early voting compared to early voting in 2012, when President Obama lost the state to Mitt Romney by 2 points.

Rep. G.K. Butterfield, a Democrat from the northeastern portion of the state and the chairman of the Congressional Black Caucus, attributed the drop mostly to Hurricane Matthew, the storm that swept across the state's coastal counties in September and displaced thousands of African American voters, who still have not returned to their homes.

Other Democrats have worried that changes to the state's early voting laws, along with court fights over those changes, have led to confusion over when and how to vote in North Carolina this year. In 2013, the Republican-led state legislature reduced early voting days and hours, required a photo i.d. to vote, and eliminated same-day registration. Much of the law was overturned, but early voting locations were significantly reduced in some counties.

The silver lining for North Carolina Democrats still worried about African American turnout was a last-minute surge in the final two days of early voting, which adjusted the drop among black voters to 9% from a projected drop of 25%.

Butterfield said Tuesday morning that the Clinton camp, as well as the DNC and DSCC had upped their spending on African American turnout efforts after he raised concerns about it several weeks ago. As a result, he said 45% of eligible African Americans in North Carolina have turned out so far in 2016, the same rate as white voters.

Butterfield was confident the African American vote would surpass 2012 when all the votes are counted, but added, "All of this suggests it's going to be a long night."

—Patricia Murphy