(CNN) Democratic senators facing tough races in Republican-leaning states are the target of a new ad from a Democratic group that pressures them to vote down President Donald Trump's nominee to the Supreme Court.

In a new six-figure ad campaign, Demand Justice -- a Democratic group aiming to sink Brett Kavanaugh's nomination -- will hit three red-state Democrats with ads urging them to vote against Kavanaugh because Republican pundits and television personalities have raised questions about his credentials and ties to the President's message.

The ads, which will target Sen. Joe Donnelly in Indiana, Sen. Heidi Heitkamp in North Dakota and Sen. Joe Manchin in West Virginia, will begin airing on Thursday.

Donnelly, Heitkamp and Manchin are three of the most vulnerable Senate Democrats up for re-election in 2018 and they all voted for Trump's first Supreme Court pick, Neil Gorsuch. All three also represent states Trump handily won in 2016 and their decision on Kavanaugh will be closely watched ahead of the November elections to see how they plan to run in the final weeks of the campaign.

"Meet Brett Kavanaugh: Son of a Washington lobbyist, as a judge ruled for special interests, lived the high life in Washington," the narrator says in the piece. "No wonder conservatives are upset."

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