That has left Republicans, who took control of Washington after years of vague promises to replace Obamacare, grasping to find a new health care message less than two months before midterm elections. Their inability to neutralize the pre-existing condition issue is hurting their efforts in tight races that could determine control of Congress.

“This is the killer app of Obamacare,” said Republican strategist Rick Wilson, pointing to the broad bipartisan support for the law’s health protections. “What you have to do at this point is duck and cover.”

Republicans’ dilemma is the latest sign of a radical shift in health care politics over the past year that’s jarred the GOP. Republican lawmakers’ clumsy failed efforts to replace Obamacare sent the law’s popularity surging as the potentially dangerous stakes for people with pre-existing conditions came into sharp focus.

Polls this summer showed that voters trust congressional Democrats more than Republicans on health care issues, and when it comes to pre-existing conditions, Democrats hold a 2-to-1 advantage, a Morning Consult/POLITICO poll found last week.

That margin has Democrats across the country running confidently on Obamacare for the first time since its passage in 2010, even in swing districts and deep-red strongholds still skeptical of the health care law.

In August, more than half of Democratic ads nationwide focused on health care, far outpacing the rate of GOP ads touting job growth or tax cuts combined. Democrats, including some who say the Obamacare repeal effort motivated their candidacy, have cut deeply personal ads highlighting their own health care struggles. Republican candidates, in contrast, have run far fewer health ads, and they tend to focus on Democratic support for single-payer health care or “one-size-fits-all” government solutions.

The Trump administration this summer added fuel to Democrats’ health care offensive when it joined part of a 20-state lawsuit aimed at eliminating Obamacare. While the administration isn’t asking the courts to throw out the entire health care law, it’s challenging provisions that ban insurers from rejecting coverage or charging more based on patients’ pre-existing conditions.

Democrats, who once worried the grass-roots energy that helped sink the repeal effort last year wouldn’t translate to electoral success this November, are worried no more about whether the health care issue will help them at the polls.

“It’s been a political gift,” said Brad Woodhouse of Protect Our Care, an activist group orchestrating much of the outside pressure on Republicans’ health care agenda. “Any prospect that they were going to get out of the health care box they put themselves in went away the minute this lawsuit was filed and the Trump administration weighed in.”

The Trump administration asked the court to delay a ruling until January, potentially pushing off backlash until after the midterms. However, a federal judge in Texas during oral arguments this month appeared sympathetic to the lawsuit challenging Obamacare and has promised a quick ruling.

Sensing their disadvantage on the issue, 10 Senate Republicans last month sponsored a bill that would force insurers, who routinely rejected patients with pre-existing conditions before Obamacare, to accept those patients. There was one major loophole, though: Insurers didn’t have to cover those conditions. In other words, an insurer would have to sell a health plan to someone with cancer, but it wouldn’t have to actually cover cancer treatment.

“It’s a cruel hoax and a fraud,” said Sen. Claire McCaskill (D-Mo.), who’s in a very tight re-election race against a Republican state attorney general who is part of the anti-Obamacare lawsuit. “How do you have a pre-existing conditions bill that says we’re going to protect people with pre-existing conditions, but not for their pre-existing condition? I mean, it’s embarrassing.”

Sen. Susan Collins of Maine, one of the Republicans whose “no” vote helped doom the Obamacare repeal effort, instantly shot down the new bill. Within hours of introducing the legislation, Sen. Thom Tillis (R-N.C.) was already backtracking, contending he could make improvements to bolster the bill’s protections.

“It was never intended to be comprehensive,” Tillis said in an interview last month. “This was to get the discussion going.”

But weeks later, the bill hasn’t been changed, and Republicans have stopped talking about it entirely.

Other Republicans say the threat to Obamacare’s consumer protections has been overblown by Democrats for political gain. They say Republicans should go on the offensive and highlight President Donald Trump’s expansion of cheaper health plans, which cost less than Obamacare plans because they cover less and provide fewer protections.

“Republicans know a better solution is to give Americans more options and let them choose the coverage that works best for them,” Sen. John Barrasso (R-Wyo.) wrote in an op-ed last week.

But few Republicans in competitive races are eager to make that case. Some are awkwardly trying to embrace Obamacare’s protections while still railing against the law. That’s proven an especially difficult tightrope walk for McCaskill’s challenger, Josh Hawley, and West Virginia Senate candidate Patrick Morrisey, who also is among the attorneys general backing the Obamacare lawsuit.

“The reality is that Josh Hawley has always said he wants people with pre-existing conditions to be covered,” his campaign said in response to an August ad highlighting his support of the lawsuit. “On the other hand, Sen. McCaskill is responsible for the current Obamacare mess.”

McCaskill, who’s trailing Hawley slightly in polls, is in the middle of airing 30 different ads in 30 days highlighting pre-existing conditions. Sen. Joe Manchin of West Virginia has surged to a comfortable lead by persistently attacking Morrisey on the issue, punctuated by an ad that shows Manchin him shooting a copy of the Obamacare lawsuit.

Three other Democrats in close Senate races in states Trump won — Sens. Heidi Heitkamp of North Dakota and Joe Donnelly of Indiana and Rep. Kyrsten Sinema of Arizona — are also making pre-existing conditions a central theme of their campaigns.

House Republicans are in an even tougher spot, since their chamber last year approved an Obamacare repeal bill that would have watered down the law’s consumer protections. The House legislation which Trump hailed in a Rose Garden celebration, was supposed to be the payoff of eight years of promises to replace the health care law. Instead, it was an instant liability for vulnerable incumbents dragged down by an unpopular president.

“You say you want to repeal something, it’s got to be replaced with something that is better than what you’re repealing,” said Rep. Dan Donovan of New York, one of the few Republicans who voted against repeal.

Donovan and 26 other House Republicans signed on to a resolution calling on Congress to restore pre-existing condition protections if the Trump-backed lawsuit in Texas wipes them out. That group includes some in competitive races, like Arizona’s Martha McSally and California’s David Valadao, who have faced intense criticism over their repeal votes.

Republicans lament that the focus on pre-existing conditions has drowned out their once-reliable campaign tactic of highlighting Obamacare’s flaws — or for that matter, Democrats’ national health plans that GOP candidates say are escaping much-needed public scrutiny.

“What we want is a marketplace where you can get what you want,” said Texas Rep. Pete Sessions, who’s battling a progressive Democrat in a district Hillary Clinton narrowly won in 2016. “Let’s tell the truth about [Obamacare]: It is a discriminatory, expensive system that’s one size fits all.”

Obamacare supporters, who have tried to tamp down talk of single-payer and “Medicare-for-all” this cycle to keep the focus on Republicans, aren’t slowing down in the campaign’s home stretch.

Liberal activist group Health Care Voter is running a voter mobilization campaign in the home districts of Sessions and 19 other House Republicans who voted for repeal.

Protect Our Care is also embarking on a six-week, 23-state bus tour to boost Democratic Senate candidates by highlighting the threats that it says GOP policies pose to health coverage.

“Make it about Republican sabotage, repeal and legal challenges to do away with things that people want,” said Woodhouse of Protect Our Care. “There’s nowhere in the country, no district, no state where Democrats shouldn’t be hammering away at this.”