The conservative group Club for Growth Action is spending another $1.5 million on attack against against Donald Trump, arguing the Republican front-runner isn't a real conservative.

"There's nothing conservative about proposing the largest tax hike in history," a narrator says in the ad, which is running in South Carolina a week ahead of the state's February 20 primary. "There's nothing conservative about supporting socialized, single-payer health care. There's nothing conservative about abusing eminent domain for personal gain."

Trump did, in fact, propose a major new tax in 1999, and he once supported a single-payer health care system. He still supports the use of eminent domain for private entities.

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Club for Growth similarly spent $1 million attacking Trump in Iowa before the GOP caucuses, in which Trump finished second behind Sen. Ted Cruz. The group claims its ads were effective: "There was a clear and steady decline in Trump's numbers through October," after the group started running its ads, Club for Growth Action president David McIntosh said in a statement.

"That didn't end until more than three weeks after the ads."

Trump responded to the news of the new ad on Twitter:

Nothing conservative about the Club for Growth coming into my office and demanding a $1M contribution, which naturally, they did not get. — Donald J. Trump (@realDonaldTrump) February 12, 2016

Back in September, the Club addressed the accusation that it's only attacking Trump because he didn't make a donation to their organization. The Club said that it did ask for the $1 million -- but only after Trump expressed interest in donating to the group. McIntosh also said the request for $1 million was made before Trump was a candidate.

Reiterating that it was Trump who initiated the conversation about a donation, he added that Trump "talks now about buying candidates -- he must've been mistaken and thought that he could buy the Club."