A group linked to the conservative mega-donors Charles and David Koch is preparing a digital advertising campaign in support of a centrist Democratic senator who backed a key piece of legislation their foundation supports.

Americans for Prosperity (AFP) is readying the ad blitz thanking North Dakota Sen. Heidi Heitkamp Mary (Heidi) Kathryn HeitkampCentrists, progressives rally around Harris pick for VP 70 former senators propose bipartisan caucus for incumbents Susan Collins set to play pivotal role in impeachment drama MORE, who was one of several Senate Democrats to support the recent passage of a bill rolling back Dodd-Frank regulations, mostly on community banks, CNBC reported on Friday.

Heitkamp is up for reelection this year, and was one of five Senate Democrats who trailed their GOP challengers in a SurveyMonkey poll in March.

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The move from the Koch network comes just months after it attacked Heitkamp with a $450,000 ad buy for opposing the GOP's tax-reform bill, which was signed into law in December.

"AFP is committed to working with lawmakers — regardless of party — to advance common sense reforms that help people improve their lives. At the same time, we will continue to hold members who voted against this crucial reform accountable," spokesman Tim Phillips told CNBC.

"While we don't agree with Sen. Heitkamp on everything, particularly her vote against tax relief, we commend her for taking a stand against the leaders of her party to do the right thing. We hope to find common ground and work with Sen. Heitkamp on other issues moving forward including making tax relief permanent," he added.

Heitkamp was the only Democratic senator to be invited to the White House for the signing of the bill rolling back the banking regulations, while Trump praised "a lot of great Democrats" — including Heitkamp and Sens. Jon Tester Jonathan (Jon) TesterPence seeks to boost Daines in critical Montana Senate race This World Suicide Prevention Day, let's recommit to protecting the lives of our veterans Filibuster fight looms if Democrats retake Senate MORE (Mont.), Joe Donnelly Joseph (Joe) Simon DonnellyTrump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court Momentum growing among Republicans for Supreme Court vote before Election Day MORE (Ind.) and Mark Warner Mark Robert WarnerIntelligence chief says Congress will get some in-person election security briefings Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' House approves bill to secure internet-connected federal devices against cyber threats MORE (Va.) — for introducing the bill along with Republicans last year.

“We’ve kept a lot of promises,” Trump said last week at the bill's signing. “This is truly a great day for Americans, and a great day for workers and small businesses across the nation.”