The future of the Republican effort to squash Obamacare hung in the balance Monday with Senator John McCain, whose vote is needed to pass the legislation, recovering from surgery away from Washington.
There are no votes to spare in the contentious effort to pass a new health care reform bill through Congress, where Republican leaders are desperate to fulfill President Donald Trump's campaign pledge to dismantle the 2010 reforms of his predecessor Barack Obama.
So when McCain, 80, announced that doctors in Phoenix removed a five-centimeter (two-inch) blood clot above his eye, Senate Majority Leader Mitch McConnell said he would "defer" the upcoming vote on the bill by at least a week.
Republicans hold 52 of the chamber's 100 seats, but two Republicans -- one conservative and one moderate -- have already declared their opposition. Democrats are united against the legislation.
Several others in the party have expressed reservations about the legislation, leaving it hanging by a thread just weeks before the Senate decamps for its summer recess -- a break already delayed in a bid to wrangle support for the controversial plan.
Unlike in some legislatures around the world, US lawmakers must be present in Congress to vote.
Senate leadership held to the idea that a vote was forthcoming.
"I believe as soon as we have a full contingent of senators, that we'll have that vote," number two Senate Republican John Cornyn told NBC's "Meet the Press" on Sunday.
Trump, who has had his differences with McCain, said Monday: "We hope John McCain gets better very soon, because we miss him. He's a crusty voice in Washington -- plus, we need his vote."
Spokesman Sean Spicer said the president would invite several senators to the White House later Monday to discuss the measure.
- How much recovery time for McCain? -
But questions swirled about how much recovery time McCain may need, after doctors performed a craniotomy, an opening of the skull in order to access tissue or blood near the brain.
While McCain's office said he will be recuperating in Arizona this week, neurosurgeons said typical healing may take longer.
"I think it's going to take him a few weeks to recover from this," Norberto Andaluz, a neurosurgeon and craniotomy specialist with Mayfield Clinic in Cincinnati, Ohio, told AFP.
One major factor for recovery time is the level of impact the operation had on the brain, said Andaluz, who is not involved in McCain's care.
Another issue is the underlying pathology.
Doctors removed several malignant melanomas on McCain's skin in the 1990s and 2000s, including an invasive melanoma in 2000.
Experts say McCain's latest operation suggests the possibility of a return of skin cancer. His office said test results are expected in the coming days.
Last week, he appeared to be in his usual talkative form with reporters in Congress.
- 'Simply unworkable' -
A delayed health care vote would undoubtedly complicate McConnell's effort to ram the legislation through the Senate.
Republican leaders are eager to notch a major legislative victory for Trump, but there is a pending logjam of important business in the Senate, including consideration of raising the limit on federal borrowing.
Achieving Trump's goal of ditching Obama's sweeping health care reforms has been elusive as his administration nears the six-month mark later this week.
Some fear that repealing the Affordable Care Act could adversely impact millions of Americans by effectively forcing them off of Medicaid, the health insurance program for the poor and the disabled, or making health costs soar for people with pre-existing conditions.
There is little institutional support for the bill, and even less for an amendment introduced by Senator Ted Cruz that would allow insurers to offer bare-bones plans.
"It is simply unworkable in any form and would undermine protections for those with pre-existing medical conditions, increase premiums and lead to widespread terminations of coverage," the chief executives of America's Health Insurance Plans and the Blue Cross Blue Shield Association warned in a letter to McConnell.
The House of Representatives passed its Obamacare repeal in May. But the Senate has stumbled, with Republicans in rival conservative and moderate wings finding it hard to get on board.
Democrats smell blood in the water.
Former vice president Joe Biden eviscerated the plan Monday, saying it would take "peace of mind" away from millions.
"They want to drag us back to a time -- not all that long ago -- when Americans could be denied basic health care because they were unable to afford it," he wrote in The Washington Post.
Failure to pass the bill would mark a humiliating defeat for Republicans who have spent seven years vowing to kill off Obamacare.
A Post poll released Sunday showed Americans preferred Obamacare to the Republican plan by 50 percent to 24 percent.