Washington (CNN) Endangered Republican candidates are responding to health care-focused campaign attacks with falsehoods and obfuscations -- with President Donald Trump leading the charge.

After two years of trying to repeal Obamacare outright, the President and some GOP candidates are suddenly claiming they support the Affordable Care Act's protections for those with pre-existing conditions -- even though they voted for repeal bills that would weaken them, or are suing to eliminate Obamacare altogether. Other Republicans are linking their Democratic opponents to Vermont Sen. Bernie Sanders' "Medicare for all" single-payer health insurance plan -- a way to invoke socialism to scare voters, even when the Democrats in those races have either opposed Sanders' plan or said it was infeasible.

The reason for the reversal is clear: Parts of Obamacare have turned out to be really popular, and Democrats have wielded Republican opposition to the law and other efforts to cut entitlement spending ruthlessly in campaigns for the House, the Senate and governor's offices.

"Obamacare was unpopular because it was disruptive," said former Rep. Tom Davis, a former chairman of the House GOP's campaign arm. Since the 2016 election, though, "the Republicans were the disruptive group. At this point, even getting into that mess, whoever is disruptive pays a price at the polls."

Davis said Republicans can't afford to let attacks over pre-existing conditions go unanswered. "I don't think you want to let this charge float out there, because health care is the one bill that is hurting them this year," he said.

But Republicans' tactical ducking and, at times, outright lies over their roles in efforts to unravel the current system either through legislation or in the courts has left some Democratic candidates exasperated -- and led to a new wave of Democratic attacks over the GOP's inconsistencies.

"It's one of the things that frustrates voters so much -- that they can't rely on anything they're hearing," Democratic congressional candidate Lizzie Pannill Fletcher said during in a debate Sunday night.

Fletcher, who was seen as a moderate during her primary match-up against Laura Moser, is challenging Republican Rep. John Culberson for a Houston-area House seat. In the debate, she complained that Culberson has cast her as a single-payer proponent in television ads and mailers even after her opposition to it made her politically vulnerable during the primary.

"And yet somehow, you, congressman, have authorized ads on TV saying the exact opposite of what I said," Fletcher said.

Similar scenes are playing out across the nation, as Democratic candidates who have opposed or expressed major reservations about "Medicare for all" are being cast as ardent supporters of the progressive idea.

In Michigan, Gretchen Whitmer, the front-runner in the governor's race, survived a Democratic primary in which she was targeted by progressives for opposing a state-level "Medicare for all"-style system.

But earlier this month, the Republican Governors Association in a TV ad accused Whitmer of pursing "a radical government takeover of your health care" that would double taxes and under which "your employer-priced insurance plan would be illegal."

The GOP efforts to shift the focus to "Medicare for all" come as the party's candidates frantically attempt to repel attacks over the health care issue that is at the forefront of nearly every campaign across the nation: their records on coverage for those with pre-existing conditions.

Promises to protect those with pre-existing conditions

Obamacare was built on the principle that coverage for sick people would be made affordable by putting healthy people in the same insurance pools -- and requiring everyone to buy that insurance.

Republicans spent most of Obama's presidency and the first year of Trump's presidency attempting to repeal Obama's health care law. While they offered partial replacements designed to make sure people with pre-existing conditions maintained access to coverage, nonpartisan experts said the alternatives would have made that coverage much more expensive.

It's a fundamental policy challenge that daunted GOP repeal efforts: Coverage for pre-existing conditions is among the reasons health insurance costs have increased; some of the main ways to lower those costs are to allow plans to discriminate against the sick and offer lesser coverage or to spend more tax dollars subsidizing premiums or shielding insurers from high-cost patients.

The backlash against GOP Obamacare repeal efforts began a groundswell of momentum for Democrats heading into the midterms. National polls have shown health care is the top issue on many voters' minds, and Democrats have focused most of their campaigns' television ads on health care -- largely alleging that their Republican foes have tried to undercut protections for those with pre-existing conditions.

Trump has rushed to Republicans' defense on pre-existing conditions in recent days. He penned a USA Today op-ed claiming to have "kept that promise" to protect coverage for those with pre-existing conditions. He tweeted last week he is in "total support" of maintaining those protections.

"Republicans will always protect people with pre-existing conditions," he said at a rally Saturday in Nevada.

And on Wednesday, he tweeted that Republicans will "totally protect" people with pre-existing conditions, while Democrats will not.

What Trump isn't saying: His own Justice Department is fighting in court to strike down Obamacare's protections for those with pre-existing conditions.

The department is arguing that these core tenets of Obamacare should be invalidated because Congress eliminated the individual mandate penalty. The case is part of a suit brought by 20 Republican state attorneys general and governors looking to strike down the law. Some of those attorneys general are on the ballot this year, including Josh Hawley, the Republican challenging Democratic Sen. Claire McCaskill in Missouri who has aired TV ads in which he says he and his wife learned their oldest son has a "rare chronic disease" this year, and that he supports "forcing insurance companies to cover all pre-existing conditions."

Other Republicans have followed Hawley's lead and told personal stories.

During their debate last week, Nevada Rep. Jacky Rosen, the Democrat challenging Republican Sen. Dean Heller, dared the incumbent to look into the camera and tell the family of a child with a heart defect "the truth about why you broke your promise and why you support slashing protections for pre-existing conditions."

Heller rejected the charge and said, "I wrote a replacement bill for the Republican Party. I know exactly what's in that bill and what's in that bill includes pre-existing conditions."

However, the bill Heller was referring to -- authored by a group that included GOP Sens. Bill Cassidy, Lindsey Graham, Ron Johnson and Heller -- actually weakened Obamacare's protections for those with pre-existing conditions. Had that legislation become law, states could have opted to once again allow carriers to base premiums on a person's medical history and to sell skimpier policies that don't cover Obamacare's 10 essential health benefits. Those with pre-existing conditions could have found themselves unable to afford insurance or able to only buy bare bones policies that wouldn't have covered all the treatments they need.

As Rosen pressed him on the issue, Heller insisted that health concerns in his own family meant he could be trusted despite the plain facts of his record.

"I have two grandchildren with pre-existing conditions," he said. "I think it's ridiculous, congresswoman, that you think that I wouldn't be there for the health and safety of my own grandchildren."

'All the parts matter'

Republican House incumbents and Senate candidates have often pointed to a failed Obamacare repeal effort last year as evidence that they would maintain protections for those with pre-existing conditions.

However, independent analyst after analyst has concluded that the House-passed repeal bill actually would have weakened Obamacare's protections. It would have allowed states to let insurers charge higher premiums to those with pre-existing conditions if they let their coverage lapse and if the state set up a high-risk program. It also would have let states apply for waivers to sell plans that don't cover all of Obamacare's mandated health benefits, such as maternity, mental health and prescription drugs.

The bill included $138 billion to create a stability fund to help lower consumers' and insurers' costs, including $8 billion over five years to support those with costly medical conditions, but experts said it was nowhere near enough.

The result in some states, the nonpartisan Congressional Budget Office said at the time, would be a pre-Obamacare health care landscape in which "people with high expected medical costs were often unable to obtain coverage."

"All the parts matter," said Karen Pollitz, a senior fellow at the Kaiser Family Foundation. "If you had a dam that blocked an entire river and then you took that out and then you just put back a couple of rocks, with gaps in between, it wouldn't be the same."

Still, Republicans have insisted industry and government experts are all somehow mistaken -- and that nonpartisan analyses of the GOP's bill are simply wrong.

In Arizona, Rep. Martha McSally, the Republican running against Democratic Rep. Kyrsten Sinema for the Senate, on Wednesday launched a new TV ad claiming she was "leading the fight" to "force insurance companies to cover pre-existing conditions."

The ad ignores the reality that Obamacare already forced insurers to cover those with pre-existing conditions. Democrats support keeping those protections in place; only Republicans have fought to change the law.

To explain her claims, McSally has pointed to the failed House GOP-passed bill -- including the $8 billion, which was added through an amendment McSally cosponsored.

In an email, McSally spokeswoman Torunn Sinclair acknowledged that analysts have concluded $8 billion wasn't enough, but said "these same estimates also don't account for potential savings from reducing health care costs by allowing new and innovative new ways to provide health coverage."

In Phoenix, Sinema told reporters that McSally's new ad "tries to pretend she supports protecting people with pre-existing conditions. But you can't run from your voting record in Arizona."