The anti-Trump Club for Growth is launching its first major ad campaign in Iowa and South Carolina in an effort to put a dent in President Trump’s commanding lead for the 2024 Republican presidential nomination.

Club for Growth and the former president have been on-again, off-again opponents since the 2016 campaign, when the group attacked Mr. Trump in the primaries before developing a closer relationship with the president during his term.

During Mr. Trump’s presidency, the organization, which normally plays a bigger role in GOP primaries than general elections, ramped up its spending in an attempt to secure some of the party’s more vulnerable districts in 2018 and 2020.

Now, the organization is returning to its opposition of Mr. Trump, funding a $3.6 million ad campaign in two early primary states — Iowa and South Carolina — to try to take the former president down a notch.

The ad, titled “John,” deploys a familiar tactic among anti-Trump Republicans in 2023: It simultaneously praises Mr. Trump while also questioning his electability.

“I love Donald Trump, I love what he did. Once he got in I thought it was a breath of fresh air,” the ad’s speaker says. “We definitely need someone that can freaking win, I think he’d probably lose that bet.”

This specific ad was placed by the Win it Back PAC, a recently created committee closely affiliated with the Club for Growth and managed by its long-time treasurer, Adam Rozansky.

The new ad represents the first public attack on Mr. Trump from the Club for Growth in an effort to prevent the former president from securing the nomination. The group since February has signaled it is looking to support someone other than Mr. Trump.

In March, the group invited Governor DeSantis, Ambassador Haley, Vice President Pence, Secretary Pompeo, Senator Scott, and Governor Youngkin to its annual donor retreat at Palm Beach, Florida. Mr. Trump was not invited.

Ahead of the retreat, the club’s president, David McIntosh, told reporters, “The party should be open to another candidate,” before suggesting that the GOP’s defeats in 2020 and relative lack of success in 2022 were in part due to Mr. Trump’s influence.

During Mr. Trump’s appearance at Council Bluffs, Iowa, on Saturday, he attacked the Club for Growth, saying, “They don’t like me too much, Club for No Growth. They’re more concerned with China than they are with our country.”

“DeSanctus, as I call him — the abbreviation — is a globalist sellout and Paul Ryan and Carl Rove acolyte who’s in the pocket of Wall Street donors at the Club for No Growth,” Mr. Trump said. “You know what I call them, the Club for China Growth.”

In addition to its battle against Mr. Trump, the Club for Growth has positioned itself in opposition to the National Republican Senatorial Committee, which is closely aligned with Minority Leader McConnell.

This spring, the club announced that it would be funding high-profile candidates in the GOP primaries in some of the NRSC’s top target areas in 2024.

The club is throwing $10 million behind Representative Alex Mooney in the West Virginia Senate primary, for one, even though Governor Justice would have a much better chance of defeating Senator Manchin in a general election.

The club is also backing Representative Matt Rosendal, who has already unsuccessfully challenged Senator Tester in Montana, while the NRSC is supporting veteran Tim Sheehy. 

Congressman Warren Davidson is also being recruited by the organization to throw his hat in the ring in Ohio in what is already becoming a crowded GOP field for the race to unseat Senator Brown.