Republican House leaders have delayed their planned vote on a long-promised bill to repeal and replace Obamacare, in a stinging setback for House Speaker Paul Ryan and President Donald Trump in their first major legislative test.
The decision came after Mr Trump, who ran as a master dealmaker, failed to reach agreement with a bloc of rebellious conservatives.
Moderate-leaning Republican politicians were also bailing on the legislation, leaving it short of votes.
The bill could still come to a vote in coming days, but cancelling Thursday's vote was a significant defeat.
It came on the seven-year anniversary of President Barack Obama signing the Affordable Care Act, years that Republicans have devoted to promising repeal.
Those promises helped them keep control of the House and Senate and win the White House but now, at the moment of truth, they are falling short.
"No deal," House Freedom Caucus chairman Mark Meadows said after he and his group of more than two dozen rebellious conservatives met with Mr Trump to try to get more concessions to reduce requirements on insurance companies.
The Republican legislation would halt Mr Obama's tax penalties against people who do not buy coverage and cut the federal-state Medicaid programme for low earners, which the Obama statute had expanded.
It would provide tax credits to help people pay medical bills, though generally skimpier than Mr Obama's statute provides.
It would also allow insurers to charge older Americans more and repeal tax boosts the law imposed on high-income people and health industry companies.
The measure would also block federal payments to Planned Parenthood for a year, another stumbling block for Republican moderates.
In a danger sign for Republicans, a Quinnipiac University poll found that people disapprove of the Republican legislation by 56% to 17%, with 26% undecided.
Mr Trump's handling of healthcare was viewed unfavourably by six in 10.
The survey was conducted from March 16 to 21 with a margin of sampling error of plus or minus three percentage points.
Republican leaders had targeted Thursday for the climactic vote, in part because it marks the seventh anniversary of Mr Obama's signing the measure into law.
With the House in recess awaiting the outcome of the White House meeting, C-SPAN aired video of that signing ceremony.
Democratic House Minority Leader Nancy Pelosi could not resist a dig.
"You may be a great negotiator," she said of Mr Trump. "Rookie's error for bringing this up on a day when clearly you're not ready."
In a count by the Associated Press, at least 30 Republicans said they opposed the bill, enough to defeat the measure. But the number was in constant flux amid the eleventh-hour lobbying.
Including vacancies and expected absentees, the bill would be defeated if 23 Republicans join all Democrats in voting No.
Mr Obama declared in a statement that "America is stronger" because of the current law and Democrats must make sure "any changes will make our health care system better, not worse for hardworking Americans".
Mr Trump tweeted to supporters: "Go with our plan! Call your Rep & let them know."
Tension has been building in advance of the critical vote, and a late-night meeting of moderate-leaning members in Mr Ryan's office on Wednesday broke up without resolution.
A key moderate who had been in the meeting, Representative Charlie Dent, issued a statement saying he would be voting No on the health bill.
"I believe this bill, in its current form, will lead to the loss of coverage and make insurance unaffordable for too many Americans," said Mr Dent, a leader of the Tuesday Group of moderate-leaning Republicans.
Congressional leaders have increasingly put the onus on the president to close the deal, seemingly seeking to ensure that he takes ownership of the legislation - and with it, ownership of defeat if that is the outcome.
Moderates were given pause by projections of 24 million Americans losing coverage in a decade and higher out-of-pocket costs for many low-income and older people, as predicted by the non-partisan Congressional Budget Office.