The conservative political group Club for Growth will launch new attack ads against former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE highlighting his past comments about race during his first primary debate appearance next week.

The group told Reuters that the ads will air on MSNBC and NBC stations in Des Moines, Iowa, and that the decision to launch the attack is based on internal polling of Biden. Iowa holds the nation’s crucial first caucus.

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The focus on Biden represents a view among many conservatives that the former vice president may pose the greatest general election threat to President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE out of any of the two dozen candidates running for the Democratic nomination. A slate of polls show Biden with substantial primary leads over the rest of the primary field and edges over Trump in several swing states, including Michigan, Wisconsin and Pennsylvania, which were the lynchpins of his 2016 victory.

However, the Biden campaign was hit with controversy this week after Biden touted his ability to work with Democratic segregationist senators during his time in Congress.

“At least there was some civility. We got things done. We didn't agree on much of anything. We got things done. We got it finished,” Biden said of former Sens. James O. Eastland (D-Miss.) and Herman Talmadge (D-Ga.) at a Tuesday night fundraiser.

Biden Wednesday defended himself, saying he had nothing to apologize for but that he “detested what they stood for in terms of segregation and all the rest.”

“Joe Biden’s past statements and positions on race issues present a serious challenge to his candidacy for the Democratic presidential nomination according to our polling,” Club for Growth President David McIntosh said in a statement to Reuters.

“This poll and the coming ad are designed to help voters and observers of the 2020 Democratic presidential primary understand the field as well as the strengths and weaknesses of the frontrunner, former Vice President Joe Biden.”

A Club for Growth poll found that support for Biden among voters dropped after respondents were told he previously had taken positions including opposing slavery reparations and busing of school children as part of desegregation efforts.

Biden has emerged as the crowded primary pack’s pacesetter, raking in millions of dollars in donations and topping every national poll since his April campaign launch.