American Indians tend to vote for Democrats and it's common for the party to visit reservations to encourage tribal members to vote.

Changes to North Dakota's voter ID laws came just months after Heitkamp's win in 2012 by fewer than 3,000 votes with the help of Native Americans, who make up about 5% of North Dakota's population.

The Turtle Mountain Band of Chippewa sued the state in 2016 over the ID requirements that many tribal members believed were aimed at suppressing their vote. The Republican-controlled Legislature said that had nothing to do with the change.

North Dakota law has always required street address identification, but before 2013 voters who didn't have one could sign an affidavit attesting to their eligibility. Now they must show ID with their residential address. American Indians argue that such addresses are not always evident on reservations, that many tribal members don't know their address, don't have a provable one because they're homeless or stay with friends or relatives, or can't afford to get an updated ID with a street address.

A federal appeals court last year ruled that the voter identification requirements are constitutional, siding with state officials who argued that not requiring street addresses could lead to voter fraud and people voting in the wrong district.