The Club for Growth announced Tuesday it would launch television advertisements in Iowa that call Donald Trump "the worst kind of politician." Above, Trump speaks at a rally in Dallas, Monday, Sept. 14, 2015. Reuters / Mike Stone

A conservative, free enterprise advocacy group is going on the offensive against Donald Trump. The Club for Growth is planning this week to launch a $1 million advertising campaign in Iowa with two 30-second videos that label the real estate mogul and current GOP front-runner as "just another politician," the group said Tuesday. The announcement marks the first step a major conservative group has taken to stop Trump.

The television spots highlight past comments from Trump where he identifies as a Democrat and supports seizing private property using eminent domain. "Trump wants us to think he's 'Mr. Tell-It-Like-It-Is,' but he has a record, and it's very liberal," one of the ads states, after showing a clip of Trump stating he identified with Democrats on many issues.

The Club for Growth said it expected the advertisements to ring true with its audience.

“Donald Trump has the worst [economic] record in the entire field with the possible exception of Bernie Sanders,” said David McIntosh, the group's president, according to the Hill. "We've tested the ads. ... We're confident that most people in Iowa will see these messages."

The Club for Growth's 100,000 members will back the ads against Trump because they are aligned with their principles, McIntosh said. The group has typically backed outsider candidates, like those from the tea party, but has battled against Trump throughout the summer.

"He's the worst kind of politician; he says anything to get elected than he'll do just the opposite when in office," McIntosh said, according to CNN.

The group has commissioned research to look into the candidate's liberal-leaning policy stances, while Trump has called the Club "that mafia organization of extortion," reported the Hill. Trump was referring to a letter purportedly from the group asking him for a $1 million contribution.

Trump has maintained a lead in state and national primary races for the GOP nomination. The average of national polls from Real Clear Politics has him taking 29.8 percent of the vote, leading over second-place Dr. Ben Carson at 17.8 percent and Jeb Bush at third with 7.8 percent. A Monmouth University poll released Monday found that Carson had gained significantly on Trump in New Hampshire, but the real estate mogul remained comfortably atop the poll.