The fiscally conservative advocacy group Americans for Prosperity is putting millions of dollars behind an ad-buy pressuring red-state Democrats up for reelection in 2018 to support the GOP’s tax reform proposals.

Americans for Prosperity, which is backed by billionaire Republican donors Charles and David Koch, has purchased $4.5 million of air time in three states, calling on Democratic Sens. Claire McCaskill Claire Conner McCaskillDemocratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally Missouri county issues travel advisory for Lake of the Ozarks after Memorial Day parties MORE (Mo.), Tammy Baldwin Tammy Suzanne BaldwinKeep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser Democrats seek balance in backing protests, condemning violence MORE (Wis.) and Joe Donnelly Joseph (Joe) Simon DonnellyEx-Sen. Joe Donnelly endorses Biden Lobbying world 70 former senators propose bipartisan caucus for incumbents MORE (Ind.) to support a tax code overhaul.

All three senators face reelection next year in states won by President Trump.

“People are sick of politics. I am too,” the narrator says in the video. “But fixing our broken tax system isn’t about politics — it’s about helping people. It means the powerful, the well-connected, politicians — they’ll stop benefiting from a rigged system. It means average Americans will have more to spend on what’s important to them. That’s what tax reform will do. So, what’s stopping us?”

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The ads close out by naming the three senators and accusing them of “standing in the way of a simple, fair system.” They provide a phone number for viewers to call the individual Senate offices.

The group has been working closely with the White House to shape and sell the GOP’s tax reform proposals.

Americans for Prosperity President Tim Phillips has been a frequent guest at the White House in recent weeks as the administration plots the best way forward.

The group has put about $8 million behind its tax reform efforts this year.

They also say they hosted 70 town halls in August and September, drawing in some 15,000 people. And Americans for Prosperity says it has knocked on tens of thousands of doors in the 36 states where it is up and running.

The White House, meanwhile, intends to direct heavy resources at tax reform before the end of the year in hopes of achieving its first major legislative victory.

Vice President Pence has been traveling to swing states Trump won in 2016, such as Michigan and Indiana, to push the plan.

Donnelly appeared at the event in Indiana, and conservatives are hopeful that other red-state Democrats facing reelection will get on board.