JEFFERSON CITY, Mo. >> In ads and speeches, Democratic U.S. Sen. Claire McCaskill is pounding Missouri voters with a single message: Her Republican challenger wants to end health insurance protections for people with pre-existing conditions.

The Republican, Attorney General Josh Hawley, says it’s not true and has been forced to defend himself.

Virtually the same campaign is playing out across the country in numerous races for Congress and governor, as Democrats flip the script on Republicans who ran and won in previous elections on promises to repeal former President Barack Obama’s health care overhaul.

At issue is a federal lawsuit filed in Texas by Republican attorneys general representing 20 states. It seeks to repeal Obama’s health care overhaul in its entirety.

If the Republicans succeed, it would mean an end to all aspects of the law. That includes parts of it that have grown widely popular over time, such as allowing adult children to stay on their parent’s insurance until age 26 and preventing insurers from charging older Americans far more than younger ones.

But one provision in particular — requiring insurers to cover those with pre-existing conditions — has become a central focus in races across the country, including the neck-and-neck contest for the Missouri Senate seat.

Hawley is among the Republican attorneys general who joined that lawsuit, giving McCaskill an opening to slam him at every opportunity.

She has highlighted the stories of 30 Missourians who have pre-existing conditions. Last week, her campaign launched a quiz that shows how voters’ health insurance would be affected if the Republican lawsuit succeeds.

“Hawley doesn’t have to pursue this lawsuit. And he doesn’t have to lie about it,” McCaskill wrote in a recent Facebook post. “If he was serious about keeping protections for people with pre-existing conditions, then he would take his name off the lawsuit tomorrow.”

When he joined the lawsuit in February, Hawley described the Obama health overhaul as unconstitutional and said his office will “fight to take health care choices out of the hands of DC bureaucrats and put them in the hands of families and physicians.”

Hawley insists that he still supports pre-existing condition coverage, even though those protections would go away if the lawsuit he joined succeeds. The only way that and other protections remain is if Congress swiftly passed a replacement bill, but so far congressional Republicans have been unable to agree on what such a plan would look like.

When asked by a reporter during a recent campaign stop if he’s concerned about a potential gap in protection, Hawley said no one would lose their coverage and that “Congress is going to have to act, no matter what.”

“Repealing Obamacare is the right thing to do, and I think there are ways to do that where there is no gap in coverage for folks,” he said. “Nothing is going to instantly disappear.”

He did not explain how that would be the case without Congress passing replacement legislation.

In an ad he’s running that features his two young sons, Hawley says his oldest has a pre-existing condition — a rare bone disease: “We know what that’s like,” says.

Hawley is not the only Republican who has had to defend their support for repealing Obama’s health care law while simultaneously trying to explain how they would preserve its protections for people with pre-existing conditions.

Mike Braun, the Republican challenging Democratic U.S. Sen. Joe Donnelly in Indiana, supports the GOP lawsuit while also saying Republicans should support legislation that protects pre-existing coverage. That made for a pointed moment in a recent debate.

“Mike, I can hardly believe that you can stand here and tell everybody you are for coverage of pre-existing conditions,” Donnelly said. “Stand here tonight and tell us you’ll denounce that lawsuit.”

Republicans running for governor in Connecticut, Georgia, Michigan, Ohio, Rhode Island and Wisconsin have all said they now support coverage protections for those with pre-existing conditions.

Attorney General Mike DeWine, Ohio’s Republican nominee for governor, reached back a quarter century, to a U.S. Senate debate from 1994, for evidence that he supports such protections. That’s despite DeWine joining another Republican lawsuit against the Affordable Care Act on his first day in office in 2011.

His Democratic rival, Richard Cordray, has barraged DeWine with attack ads highlighting the issue.

Wisconsin Gov. Scott Walker, who is seeking a third term, has been working for years to repeal Obama’s health care law and signed off on the state attorney general joining the lawsuit against it.

But earlier this year, Walker called for a state law that would bar insurers from denying a person health coverage due to a pre-existing condition. In talking about his support for the protections, Walker said the step was necessary because “Washington failed to act” on passing a replacement for the Affordable Care Act.

His Democratic rival, Tony Evers, launched an ad calling on Walker to drop his support for the lawsuit.

“Actions speak louder than words,” Evers said.

Protecting the most popular parts of the health care act has emerged as one of the key election issues in Republican-dominated states, such as McCaskill’s. She’s among 10 Democratic Senate incumbents running in states won by Trump.

Insurance coverage for those with pre-existing conditions “affects a lot of people, whether they’re liberal, conservative, middle-of-the-road (or) don’t care about politics,” said University of North Carolina at Chapel Hill political scientist Jason Roberts.

Hawley has proposed requiring private insurers to cover pre-existing conditions at no extra cost. Under his plan, the federal government would collect premiums from those patients and then cover insurance costs that exceed a certain amount.

McCaskill’s message: Don’t trust that from someone who is actively trying to repeal the law that already provides that exact protection.

“He wants the whole thing thrown out, and he knows there’s nothing there to back it up,” McCaskill said during a September debate. “Nothing.”