“The new voter suppression in the 21st century is all this voter confusion,” said Nina Turner, the Democratic candidate for Ohio secretary of state, an office that administers elections.

Her opponent, the Republican incumbent Jon Husted, said that Ohio still had 28 days of early voting, more than the majority of states, and that only “a few extreme voices on the political left” opposed the one-week cutback.

In Wisconsin, voting officials are scrambling to enforce a voter identification requirement after the United States Court of Appeals for the Seventh Circuit declined to take up the case last month. It could affect the tight race between Gov. Scott Walker, a Republican who supports the voter ID law, and Mary Burke, his Democratic challenger. Civil liberties groups appealed the case to the Supreme Court, predicting “chaos at the polls” because there is not enough time for 300,000 registered Wisconsin voters without acceptable IDs, many of them minority residents, to obtain the documents. A Marquette Law School poll late last month found that 18 percent of likely voters did not know an ID is needed to vote.

In North Carolina, where a crucial Senate race is underway, Gov. Pat McCrory, a Republican, is appealing to the Supreme Court a lower-court ruling that blocked parts of the state’s voting law, one of the country’s most restrictive.