A Supreme Court decision last week that lets Ohio reduce its early-voting period to 28 days from 35 drew a sharp rebuke Monday from U.S. Attorney General Eric Holder, who sees racial animus at work.

In a video posted on the Justice Department’s website, Mr. Holder explains that the Ohio voting restrictions “significantly reduce opportunities for early voting--opportunities that had in the past been heavily used by African-American voters.” Ohio, he said, illustrates how some states are enacting “troubling new measures that...