The law has more headaches than just "In Play" asks some of The Washington Post's top political reporters to explain. (The Washington Post)

The political fallout from the botched launch of the health-care law is presenting congressional Democrats with one of their toughest tests of party loyalty in the five years of the Obama administration.

House Republicans are expected to pass a bill Friday that could dramatically undermine the law. And after years of trying to impale the initiative, GOP leaders are hopeful that the political turmoil over the rollout will provide them the support of a sizable bloc of Democrats.

In the Senate, moderate Democrats facing reelection battles next year have assembled legislative alternatives designed to fix some of the problems and provide political cover for themselves.

Into this caustic mix stepped President Obama with his announcement Thursday that he will allow insurance companies to continue offering plans that do not meet the new law’s requirements.

The move was a direct response to the political eruptions that followed news that insurance carriers were canceling policies after the president had promised that people would be able to keep them if they so desired. “If you like your doctor, you keep your doctor” became something of a mantra for Obama.

President Obama explained how Americans who wish to keep their health plans can work to do so under his signature health-care law during a speech Friday. (The Washington Post)

At one point during what amounted to an hour-long mea culpa, Obama even apologized on behalf of the many Democratic lawmakers who repeated those assurances to the voters.

“They were making representations based on what I told them and what this White House and our administrative staff told them, and so it’s not on them, it’s on us,” Obama said in the White House Briefing Room.

As the president finished answering questions, the White House’s full-court press continued on Capitol Hill. Denis McDon­ough, Obama’s chief of staff, led several senior officials into nearly four hours of meetings.

First, they ducked in with the 55-member Senate Democratic caucus. They tried to calm the group and pleaded for time to try to repair the damage without any legislative interference, pledging to fix the federal Web site that opened to disastrous reviews on Oct. 1.

McDonough and his group then darted across the Capitol and down into a basement room where nearly 200 House Democrats had assembled, delivering the same message.

In particular, they urged House Democrats to not support Friday’s GOP bill, which would allow people to keep their old health insurance by extending the “grandfather provisions” of the health-care law to include plans purchased after the law was adopted in 2010. Democrats worry that that would keep millions of people out of the exchanges and decimate the act.

A large number of such defections would be a policy blow to the law, but it would be an even more significant political gut punch to the president. The White House on Thursday night said the president would veto the GOP bill if it came to his desk.

For now, the White House appears to have calmed the nerves of anxious Democrats, but Obama’s allies warned that the support was not open-ended. Instead, Obama’s once-loyal supporters on Capitol Hill gave a qualified, trust-but-verify commitment.

“The president’s guidance was welcome and well received, but we still may have to fashion some legislation, and we’re going to continue to work that,” Sen. Mary Landrieu (D-La.), lead sponsor of a bill similar to the House draft, told reporters after the McDonough meeting.

Landrieu epitomizes the political and policy problems that Democrats are confronting. Facing a difficult reelection race in 2014, Landrieu was one of the final crucial votes for the health-care law in 2009, and then gave her support only after receiving special provisions for her state.

At every turn, Republicans are pounding Landrieu for her health-care vote, as well as a crop of Democrats who rode into office with Obama in 2008 and face reelection next year: Sens. Mark ­Begich (Alaska), Kay Hagan (N.C.), Jeff Merkley (Ore.) and Jeanne Shaheen (N.H.). Merkley and Hagan signed on to Landrieu’s bill, as did another endangered Democrat, Sen. Mark Pryor (Ark.), who first won office in 2002.

Having cast those big votes with Obama, the Democrats know that it will be very difficult to distance themselves from the president next fall. Landrieu is particularly sensitive to any accusation that she is running from the president, something Republicans said when she did not attend an Obama event last week in New Orleans.

A scheduling conflict kept her away, but she flew with him on Air Force One and made an appearance at the airport. “I waved from the top of the steps. Did you see me smiling? If I wanted to hide, I wouldn’t have been there,” she told reporters earlier this week.

Democrats have a five-seat advantage in the Senate, but with seven seats being closely contested next year, the majority control is up for grabs.

On Thursday, the National Republican Senatorial Committee issued a news release attacking the Democratic senators who voted for the bill as either “incompetent or dishonest.”

House Republicans issued research showing the dozens of House Democrats who had uttered almost the exact same phrase as Obama, trying to shame them into supporting legislation Friday that Rep. Fred Upton (R-Mich.) crafted to give insurers even more freedom to keep selling plans to individuals.

Democrats believe Upton’s bill would keep too many people out of the insurance exchanges and lead to much higher premiums on those participants, potentially crippling the law. Some Democrats said that their word in supporting the 2010 law was enough to support Upton’s plan.

Rep. Nick J. Rahall II (W.Va.), a 19-term veteran targeted in 2014 by Republicans, said ads are running against him in his district based on the president’s promise to allow Americans to keep their health-care plans.

“I’m concerned about my integrity with voters that have returned me [for] 38 years. They know me enough to know I wouldn’t purposely mislead them and that I’m an honest, straight shooter,” he said. “They have that confidence in me, and I want to continue for them to have that confidence in me. I just need to find the answers myself.”

Sen. Joe Manchin III (D-W.Va.), a popular former governor, supports Landrieu’s effort and said he will need to see how Obama’s announcement works with the insurance markets.

House Democrats said Thursday’s White House presentation was helpful because they finally saw their concerns addressed.

“A lot of us felt there was no sense of urgency to get this done,” said Rep. Mike Doyle (Pa.), a reliable liberal vote, who had publicly threatened to back the Upton bill unless the White House and leadership responded. Instead, Democrats are crafting an alternative to the Upton bill and, along with the administrative fix, will have enough political cover to go home and defend themselves — for now.