A Democratic group is wading into the Republican Senate primary in Ohio with a new television spot aimed at promoting the conservative credentials of Bernie Moreno, a Cleveland-area businessman who has been endorsed by former President Donald J. Trump.
The spot criticizes Mr. Moreno as ultraconservative and too aligned with Mr. Trump. But by running the ad in the final week of the primary, those critiques are likely to be viewed as badges of honor by Republican primary voters, a tactic Democrats have employed in other races in recent years.
A group called Duty and Country is spending roughly $2.7 million on the ad, which is set to run across the state, according to AdImpact, a firm that tracks advertising.
The group is funded largely through the Senate Majority PAC, the principal super PAC supporting Democratic efforts to maintain control of the chamber.
Mr. Moreno is running for the Republican nomination against State Senator Matt Dolan and Ohio’s secretary of state, Frank LaRose. The winner will face Senator Sherrod Brown, the Democratic incumbent.
“Democrats constantly underestimate the America First movement at their own peril,” said Reagan McCarthy, communications director for Mr. Moreno. “They thought President Trump would be easy to beat in 2016 and then they got their clocks cleaned when he demolished Hillary Clinton. The same thing is going to happen to Sherrod Brown this year.”
Mr. Moreno has struggled to pull away from his primary challengers despite the endorsement from Mr. Trump and others, including Senator J.D. Vance, a Trump-backed Republican who was elected in 2022. Mr. Moreno won their backing by embracing hard-line conservative positions that Democrats view as potentially easier to run against in a general election.
“When Ohio voters head to their polling place, they deserve to know the truth about Bernie Moreno — and the truth is that Moreno is a MAGA extremist who embraced Donald Trump just like he embraced his policies to ban abortion nationwide and repeal” the Affordable Care Act, said Hannah Menchhoff, a spokeswoman for Senate Majority PAC.
Republicans need to flip two seats to win back power if President Biden is re-elected, but just one if the White House returns to Republican hands. Republicans already are expected to gain one seat in West Virginia after Senator Joe Manchin III, a Democrat, announced he would not seek re-election.
In the California Senate primary last month, Representative Adam Schiff, a Democrat, ran a spot describing Steve Garvey, a Republican and a former Major League Baseball player, as too conservative. Mr. Schiff and Mr. Garvey will face off in November in their deep-blue state.
In the Pennsylvania governor’s race in 2022, the Democrat, Josh Shapiro, ran an ad in the Republican primary playing up the conservative credentials of Doug Mastriano, the Trump-backed candidate in the race. Mr. Mastriano won and Mr. Shapiro easily defeated him to win the governor’s office.