A vulnerable Senate Democrat is targeting her Republican opponent over ObamaCare in a new ad released Thursday.

Sen. Heidi Heitkamp Mary (Heidi) Kathryn HeitkampHarris faces pivotal moment with Supreme Court battle Centrists, progressives rally around Harris pick for VP 70 former senators propose bipartisan caucus for incumbents MORE (D-N.D.), who is running for reelection in a state won by Donald 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 in 2016, released an ad highlighting GOP Rep. Kevin Cramer Kevin John CramerAbortion stirs GOP tensions in Supreme Court fight Momentum growing among Republicans for Supreme Court vote before Election Day On Paycheck Protection Program, streamlined forgiveness is key MORE's votes to repeal ObamaCare.

The ad features a woman named Denise who has heart disease.

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"Mr. Cramer, I don't know why you voted to let insurance companies go back to denying coverage for pre-existing conditions but I know Heidi would never do that," Denise says.

Cramer voted to repeal ObamaCare 65 times, Heitkamp's campaign said.

“Heidi has worked across the aisle to improve the current law to make health care more accessible and affordable for North Dakotans," said Libby Schneider, Heidi for North Dakota campaign manager.

"In stark contrast, Kevin Cramer has spent his time in Washington voting 65 times to repeal or undermine the health care law — without offering a single solution to make it work better for North Dakotans."

North Dakota Republican Party Communications Director Jake Wilkins said he's not concerned about Heitkamp's attacks on health care.

"Heidi Heitkamp's repeated lies about Cramer's stance on pre-existing conditions won't work," he said.

"Heitkamp's support for Obamacare has saddled North Dakotans with higher costs, worse care, and fewer options, and voters will remember that in November."

Democrats believe health care is a winning issue for them heading into the midterms, where they hope to win back control of the House and the Senate. They are facing a tough road in the upper chamber where they have 10 members defending in states that were won by Trump in 2016.

While Republicans campaigned for years on promises to repeal the health care law, they have since backed off of that campaign issue after failing to pass repeal bills several times last year.