Sen. Heidi Heitkamp (D-ND) faces one of 2018’s most difficult reelection campaigns. Donald Trump won her state of North Dakota by nearly 30 points in 2016. He still enjoys a positive approval rating there. The early polls show Heitkamp and her Republican opponent, Rep. Kevin Cramer, neck and neck in the November general election.

So as we round the corner and head into the fall, what is Heitkamp focusing on? Obamacare — and preexisting conditions, specifically.

The spot features Denise, a North Dakotan with a heart condition, and reminds voters of Heitkamp’s personal stake in prohibiting health insurers from discriminating against people with preexisting conditions: The senator is a breast cancer survivor.

The ad, at its essence, positively contrasts a red-state Democrat’s support for Obamacare — imagine reading that sentence in 2010 or 2014 — with Cramer’s vote for the House’s Obamacare repeal bill last year, which would have rolled back the law’s ironclad protections for preexisting conditions.

It’s all the proof you need to know that 2018 will be the inverse of the past two midterm cycles: Democrats are relying on Obamacare to carry them in tough races rather than Republicans exploiting it to bring them down.

Health care is among voters’ top issues this year, and they trust the Democrats more than Republicans. Obamacare’s preexisting conditions protections are very popular with and particularly important for women, a fact further highlighted by a Heitkamp ad that spotlights two women.

You won’t find this message in just North Dakota either. Democrats are spending more money on ads for health care, according to the Cook Political Report, than any other issue.

Like Heitkamp, Democratic Sen. Tammy Baldwin has emphasized her personal history with preexisting conditions — she’s had one since she was 9 — in the Wisconsin Senate campaign.

In West Virginia, Sen. Joe Manchin (D-WV), also up for reelection in a tough race, penned an op-ed earlier this summer that criticized the Trump administration for attacking preexisting conditions.

”It is important for everyone to have health insurance because your health can change in a blink of an eye,” he wrote, “and West Virginians with pre-existing conditions like these are the ones that need health insurance the most.”

In Indiana, Sen. Joe Donnelly (D-IN) — maybe the single-most vulnerable Democrat this cycle — called the preexisting conditions rules “one of the best parts of the Affordable Care Act” in his own digital video, and chided his Republican opponent, Mike Braun, for claiming that he supports them too.

The Trump administration has guaranteed that this will be a big issue in the fall by arguing in a federal lawsuit (which has hearings scheduled for September 10) that the preexisting conditions protections should now be unconstitutional since the individual mandate was repealed in the GOP tax bill.

That lawsuit, and the pending Supreme Court nomination for Judge Brett Kavanaugh, will present an interesting dilemma for Heitkamp, Manchin, Donnelly, and other Democrats trying to toe a fine line between contrasting with Republicans without completely severing themselves from Trump.

Though the real swing vote will likely be Chief Justice John Roberts, given his history of upholding Obamacare. But some Senate Democrats and activists are treating the Kavanaugh nomination as an existential threat to the ACA if this new lawsuit reaches the Supreme Court with the new justice on it.

The case’s hearings will start almost simultaneously with the Kavanaugh hearings in the Senate. Given the campaign messages that Heitkamp and other Democrats are relying on, and the uncertain status of the Kavanaugh whip count, you could imagine health care being the basis by which these senators decide to oppose his nomination.

Or they might not want to confront Trump that directly, so shortly before the election.

But regardless, Heitkamp and the rest are clearly betting that Obamacare will be a boon, not a bust, for Democrats in 2018.

vox-mark Sign up for the newsletter VoxCare Get our newsletter in your inbox once a week. Email (required) By signing up, you agree to our Privacy Notice and European users agree to the data transfer policy. For more newsletters, check out our newsletters page Subscribe

This story appears in VoxCare, a newsletter from Vox on the latest twists and turns in America’s health care debate. Sign up to get VoxCare in your inbox along with more health care stats and news.