Larry Harmon, a 59-year-old software engineer and Navy vet, went the polls in 2015 in his hometown of Kent, Ohio, to vote on a state ballot initiative. But poll workers told him he was no longer registered and could not vote.

“I felt embarrassed and stupid at the time,” Harmon told Reuters. “The more I think about it, the madder I am,” he said.

Harmon voted for Barack Obama in 2008 but had not returned to vote until 2015. He later learned that he was purged from the rolls in Ohio for “infrequent voting” because he had not voted in a six-year period, even though he hadn’t moved or done anything to change his registration status. The same thing is now happening to tens of thousands of voters across the state. The fear is that voters who cast ballots in 2008 but have not participated since, particularly first-time voters for Obama, will show up in 2016 to find that they are no longer registered. Ohio has purged more voters over a 5-year period than any other state.

At least 144,000 voters in Ohio’s three largest counties, home to Cleveland, Columbus, and Cincinnati, were purged since the 2012 election, with voters in Democratic-leaning neighborhoods twice as likely to be removed as those in Republican-leaning ones, according to a Reuters analysis by Andy Sullivan and Grant Smith. That includes 40,000 voters purged in Cleveland’s Cuyahoga County, where the GOP convention is taking place this week. These cities are heavily Democratic, with large minority populations, and there’s a clear partisan and racial disparity to the state’s voter purge.

According to Reuters:

In Cleveland’s Cuyahoga County, 5 percent of voters in neighborhoods that backed Obama by more than 60 percent in 2012 were purged last year due to inactivity, according to the Reuters analysis of the voter lists. In neighborhoods where Obama got less than 40 percent of the vote, 2.5 percent of registered voters were removed for that reason.

In Franklin County, home to the state capital Columbus, 11 percent of voters in Democratic-leaning neighborhoods have been purged since 2012 due to inactivity. Only 6 percent of voters in Republican-leaning neighborhoods have been purged.

The disparity is especially stark in Hamilton County, where affluent Republican suburbs ring Cincinnati, which has one of the highest child-poverty rates in the country.

In the heavily African-American neighborhoods near downtown, more than 10 percent of registered voters have been removed due to inactivity since 2012. In suburban Indian Hill, only 4 percent have been purged due to inactivity.

Ohio’s Republican Secretary of State Jon Husted says more than 2 million voters have been purged since 2011. From 2011 to 2014, 846,000 were struck for infrequent voting and 480,000 for moving. “Of the 2 million purged, 1.2 million are questionable purges,” says State Representative Kathleen Clyde, a Democrat from Kent who has led opposition to the purge. “We shouldn’t be playing games with people’s voter registrations and fundamental right to vote. Instead we should be trying to get them to the polls.”

The purge works like this: If a voter misses an election, Ohio sends them a letter making sure their address is still current. If the voter doesn’t respond, Ohio puts them on an inactive list, and if the voter doesn’t vote in the next two elections they are removed from the rolls.

An analysis by Clyde’s office found that 666 voters in Cincinnati’s Hamilton County had their ballots rejected in 2015 because they were listed as “Not Registered.” Fifteen percent of those voters were purged just a few months before the election. “Based on this finding from only one election in only one county, it is safe to assume that across the state over multiple elections, tens of thousands of purged voters have had their ballots thrown out,” Clyde said. “Even worse, these voters do not even know that their votes were rejected because they are not notified when that happens.”

Larry Harmon, one such voter, became a plaintiff in a lawsuit challenging the purge filed by Demos and the ACLU of Ohio. “As a result of these violations, numerous Ohioans have been disenfranchised in recent elections, and many more face the threat of disenfranchisement in the 2016 Presidential Election and future elections,” the lawsuit stated.

In late June, federal district court Judge George C. Smith, a Reagan appointee, ruled for the state, saying that “Ohio’s procedures of maintaining the voter registration rolls ensure the integrity of the election process.” Smith ruled that Ohio had not violated the National Voter Registration Act, which forbids purging based on infrequent voting, because the infrequent voters had failed to respond to a mailing sent by the state warning that their registrations would be suspended—a questionable interpretation of the law. The Sixth Circuit court will hear an appeal on July 27.

This isn’t the first time a controversial voter purge in Ohio has attracted scrutiny in the midst of a hotly contested presidential election. In 2004, the Ohio Republican Party sent a mailing to 232,000 newly registered voters, urging them to vote Republican. When 35,000 mailers were returned as undeliverable, the GOP tried to purge those voters from the rolls. As I reported in my book Give Us the Ballot, “more than half the challenged voters lived in Ohio’s two most populous counties—Cuyahoga (Cleveland) and Franklin (Columbus)—which were overwhelmingly Democratic and heavily minority.” The DNC sued the RNC and a federal court blocked the purge, ruling that voters “faced irreparable injury” to their “constitutional right to vote.”

But Republican-led voter purging efforts proved disastrous during the 2000 election in Florida, when the state wrongly labeled 12,000 registered voters as ex-felons and scrubbed them from the voter rolls—a number that was 22 times George W. Bush’s 537-vote margin of victory. That election taught the unfortunate lesson that small manipulation to the country’s voting laws could make a big difference in close elections. History could repeat itself in 2016.