Candidates spent a last full day of campaigning around Ohio on Monday before voters select a new governor and decide a U.S. Senate race and some closely contested congressional seats.
Voters also will decide a constitutional amendment Tuesday that proposes reducing sentences for possession of certain drugs, among other measures.
Former Attorney General Eric Holder appeared with Democratic attorney general candidate Steve Dettelbach in Cleveland on Monday, a day after stumping for Dettelbach, Democratic gubernatorial candidate Richard Cordray and other Democrats alongside Ohio-born singer-songwriter John Legend.
Cordray is locked in a tight gubernatorial race with Republican Ohio Attorney General Mike DeWine, a former U.S. senator and lieutenant governor who's one of Ohio's most well-known politicians. Cordray previously served as Ohio attorney general and director of the Consumer Financial Protection Bureau.
Mandi Merritt, a spokeswoman for the Republican National Committee, criticized Democrats for rolling on Holder and Legend in the campaign's final days, calling Holder a "controversial Obama alumnus" and Legend a "west-coast rockstar" in a statement.
She said voters should ask "do we want to move forward with Republican results, or do we want to move backward with Democrat resistance."
Republicans were making their final arguments in the bellwether state as Democrats were optimistic that the midterm momentum was moving in their favor.
GOP President Donald Trump was scheduled to appear with DeWine and his wife, Fran, at a get-out-the-vote rally at Cleveland's I-X Center later Monday.
Cleveland police said they found nothing after a bomb threat was called in Monday morning to a business near the center. They have not said whether the threat related in any way to Trump. Evacuated employees were allowed to return to the building after the search.
Republican Ohio Gov. John Kasich, a vocal Trump detractor, was out of state and not planning to attend the Trump rally. He had a line-up of television appearances scheduled, beginning with ABC's "The View" and winding up with Comedy Central's "The Daily Show with Trevor Noah."
DeWine embraced Kasich's backing last week at a joint rally and in an ad, as what was initially touted as an unbeatable Republican ticket with running mate Jon Husted, the secretary of state, has struggled to pull comfortably ahead in polls.
Republican U.S. Rep. Jim Renacci also was slated to appear at Trump's rally in Cleveland on Monday, in his bid to unseat Democratic U.S. Sen. Sherrod Brown, who polls have favored to win.
In a closely contested U.S. House race in central Ohio, Democrat Danny O'Connor and former GOP state Sen. Troy Balderson were making their final pitches to voters in a rematch for Ohio's 12th District. Democrat Aftab Pureval, the Hamilton County clerk of courts, was challenging GOP U.S. Rep. Steve Chabot in the 1st District in southwest Ohio.
Husted's office reported an estimated 1.2 million absentee ballots had been requested and more than 737,000 absentee ballots cast as of Wednesday. That's a 36 percent increase in requests and a nearly 60 percent increase in absentee ballots cast over 2014, the last time Ohio elected statewide officeholders.
A panel of federal judges ruled last week that Ohioans removed from voter registration rolls for not casting ballots over a six-year period will be able to participate in Tuesday's election.
Husted also issued an order that the ACLU said should assure that some 20,000 voters in Butler County potentially affected by a printing error on ballot envelopes would have their votes counted.