It’s health care, stupid.

In this year’s midterm elections, that’s the motto of Democrats seeking to upend the Republican majority in Congress. After the disastrous GOP attempt to undo the Affordable Care Act last year, Republicans are standing by their “repeal and replace” mantra but insist they would provide coverage for those with pre-existing conditions. Democrats, meanwhile, have capitalized on Obamacare’s newfound popularity, especially in red state Senate races where President Trump remains popular, and are playing aggressive defense as Democratic incumbents try to onto hold their seats. And the timing for this strategy couldn’t be better: Numerous national polls show health care topping the economy as the number one issue for voters this election cycle.

Several factors have changed the issue of health care from one Democrats couldn’t run far enough from to one they are embracing with open arms. Health policy analysts say insurers have largely seen the market stabilize after years of uncertainty about pricing and predict that the massive premium hikes of years past are unlikely to return this enrollment cycle. This might explain why a Fox News poll from August shows Obamacare is more popular among voters than the GOP tax cuts. Another survey shows that, overall, Americans prefer the Democrats to handle the issue of health care over Republicans by 18 percentage points, according to an NBC News/Wall Street Journal poll from April.

The issue has played prominently in two states where Republicans are hoping to oust Democratic senators: North Dakota and West Virginia. A poll in West Virginia out Monday showed 20 percent of respondents chose health care as their top issue, with the economy coming in second at 14 percent. A North Dakota poll from over the summer had similar findings, with health care falling just two points behind the economy as the most important issue for voters; another poll this week showed health care right behind nominees for the Supreme Court. Both are rural states where small-business owners and farmers have suffered under high health care premiums the past few years. But many in these states, particularly West Virginia, which has struggled with a brutal opioid epidemic, fear coverage loss for pre-existing conditions.

Sens. Heidi Heitkamp and Joe Manchin have hit the issue hard on the campaign trail. Manchin’s campaign said health care is the biggest concern they hear from voters, who worry that a pending Obamacare lawsuit could jeopardize their coverage. Manchin’s Republican challenger, Attorney General Patrick Morrisey, joined the suit with 19 other states to argue that Obamacare is unconstitutional. The issue was a feature of a Manchin campaign ad last month.

“Now the threat is Patrick Morrisey’s lawsuit to take away health care from people with pre-existing conditions,” said the two-term senator in the spot, which showed him shooting at a document representing the lawsuit — harkening back to a 2010 ad on climate change where he employed a similar tactic. “He is just dead wrong and that ain’t gonna happen,” Manchin added.

Morrisey’s campaign denied Manchin’s allegation and said the Democratic incumbent cares more about his party than West Virginians. “There is no debate over coverage for pre-existing conditions, but that won't stop liberal Joe Manchin and his Washington special interests allies from launching false attacks,” said Nathan Brand, campaign spokesman for Morrisey.

In North Dakota, Heitkamp and her Republican challenger, Rep. Kevin Cramer, have also sparred over coverage for those with pre-existing conditions. Heitkamp has touted her role in the Bipartisan Health Care Stabilization Act — widely known as the Alexander-Murray plan — which aimed to fund cost-sharing reduction payments while also giving states more flexibility for insurance coverage plans. The bill has yet to be voted on, but Trump discontinued marketplace stabilization payments last October.

Health care is also personal for Heitkamp — a breast cancer survivor — which she mentioned over the summer in a campaign ad featuring a constituent with a heart condition. “Like 300,000 North Dakotans, Denise has a pre-existing condition,” said the first-term senator in the video. “That used to mean no health insurance. For me, it’s breast cancer. For Denise, it’s heart disease.” Ads from liberal groups such as Majority Forward and the Democratic Senatorial Campaign Committee have also flooded the state, taking aim at Cramer’s record on health care.

Cramer voted to repeal and replace Obamacare in the House and supports the lawsuit against the ACA — which North Dakota also joined — and has stood by these positions on the campaign trail. His campaign did push back on the allegation -- expressed in an ad last month -- that he did not support covering those with pre-existing conditions. “Here’s the truth,” says the narrator in the spot, according to Roll Call. “Kevin Cramer voted for guaranteed coverage for pre-existing conditions, and Heidi’s ads attacking Kevin on health care don’t pass the smell test.”

The focus on health care has yielded mixed results for Democratic candidates. While Manchin has held a steady lead throughout the race, Heitkamp is underwater. A Fox News poll from Wednesday shows her down 12 points against Cramer, and RealClearPolitics now rates the race as “leans Republican,” with Cramer up by nearly nine points in the RCP poll average. Manchin, on the other hand, leads by more than nine points in the RCP average and the race is slated as “leans Democratic.”

Polls still to come will also need to take into account the chaotic nomination of Brett Kavanaugh to the Supreme Court. When RCP asked Cramer’s campaign about the health care issue, a spokesman responded that the Supreme Court outranked health care for voters at the moment. And Heitkamp’s announcement Thursday that she intends to vote against Kavanaugh could further add to her deficit. But as open enrollment is set to begin just before Election Day, this pocketbook issue of health insurance appears likely to be very much on voters’ minds as they cast their ballots.