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COLUMBUS, Ohio (AP) — Three-term Democratic U.S. Sen. Sherrod Brown of Ohio faces perhaps the toughest reelection challenge of his career Tuesday in the most expensive Senate race of the year as control of the chamber hangs in the balance.

Brown, 71, one of Ohio’s best known and longest serving politicians, faces Republican Bernie Moreno, 57, a Colombian-born Cleveland businessman endorsed by former President Donald Trump, in a contest where spending has hit $500 million.

Trump appeared in ads for Moreno in the final weeks of the contest, while Democratic former President Bill Clinton joined Brown for a get-out-the-vote rally in Cleveland on Monday.

Brown has defeated well-known Republicans in the past. In 2006, he rose to the Senate by prevailing over moderate Republican incumbent Mike DeWine, another familiar name in state politics.

DeWine, who is now Ohio’s governor, parted ways with Trump in the primary and endorsed a Moreno opponent, state Sen. Matt Dolan — though he got behind Moreno when he won. In October, former Gov. Bob Taft, the Republican scion of one of Ohio’s most famous political families, said he was backing Brown.

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Ohio has shifted hard to the right since 2006, though. Trump twice won the state by wide margins, stripping it of its longstanding bellwether status.

Brown’s campaign has sought to appeal to Trump Republicans by emphasizing his work with presidents of both parties and to woo independents and Democrats with ads touting his fight for the middle class. In the final weeks of the campaign, he hit Moreno particularly hard on abortion, casting him as out of step with the 57% of Ohio voters who enshrined the right to access the procedure in the state constitution last year.

Moreno, who would be Ohio’s first Latino senator if elected, has cast Brown as “too liberal for Ohio,” questioning his positions on transgender rights and border policy. Pro-Moreno ads portray Brown as an extension of President Joe Biden and his vice president, Democratic presidential nominee Kamala Harris, particularly on immigration. That exploded as a campaign issue in the state after Trump falsely claimed during his debate with Harris that immigrants in the Ohio city of Springfield were eating people’s pets.

Brown remained slightly ahead in some polls headed into Election Day, though others showed Moreno — who has never held public office — successfully closing the gap in the final stretch. Trump’s endorsement has yet to fail in Ohio, including when he backed first-time candidate JD Vance — now his running mate — for Senate in 2022.

As Moreno and his Republican allies consistently outspent Democrats during the race, they aimed to chip away at Brown’s favorability ratings among Ohio voters. He remains the only Democrat to hold a nonjudicial statewide office in Ohio, where the GOP controls all three branches of government.