After meeting with President Trump at the White House, Mr. McConnell told reporters that if Republicans could not come to an agreement, they would be forced to negotiate a deal with Senator Chuck Schumer of New York, the Democratic leader.
“The status quo is simply unsustainable,” Mr. McConnell said. “It’ll be dealt with in one of two ways: Either Republicans will agree and change the status quo, or the markets will continue to collapse, and we’ll have to sit down with Senator Schumer. And my suspicion is that any negotiation with the Democrats would include none of the reforms that we would like to make.”
Republicans have promised for seven years to repeal the health law, President Barack Obama’s signature domestic achievement. But Mr. McConnell’s announcement on Tuesday was yet another major stumble in the unsteady quest by Republican congressional leaders to deliver a repeal bill to the desk of Mr. Trump, who has yet to sign his first piece of marquee legislation.
Mr. McConnell, the chief author of the Senate repeal bill, can afford to lose only two of the 52 Republican senators, but more than a half-dozen have, for widely divergent reasons, expressed deep reservations about the bill.
Mr. Trump, meeting with Republican senators at the White House, declared, “We’re getting very close.”
“This will be great if we get it done,” he said. “And if we don’t get it done, it’s just going to be something that we’re not going to like, and that’s O.K., and I understand that very well.”
Mr. McConnell wrote his bill behind closed doors, betting he could fashion a product that would show significant improvement over the bill that was narrowly approved by the House last month. And he laid out an aggressive timeline for its passage, hoping to secure Senate approval roughly a week after unveiling the legislation.
Yet on Tuesday, just five days after releasing the bill, Mr. McConnell had to bow to reality: Republican senators were not ready to move ahead with the bill.
At least a small number might never be — raising questions about whether Mr. McConnell will be able to win over the votes for passage.
“It’s difficult for me to see how any tinkering is going to satisfy my fundamental and deep concerns about the impact of the bill,” said Senator Susan Collins, Republican of Maine, who was among the lawmakers prepared to vote against taking up the bill this week.
Mr. McConnell and his leadership team are hoping to replicate the feat of Speaker Paul D. Ryan, who revived the House’s repeal bill and pushed it to passage six weeks after it appeared to be dead.
“I would hope, by the end of the week, that we have reached basically a conclusion with regard to the substance and the policy of this,” said Senator John Thune of South Dakota, a member of the Senate Republican leadership.
Then, he said, it is just a question of timing.
Democrats are unified against the repeal bill, but they were not celebrating on Tuesday.
“The mantra on our side is never to underestimate Mitch McConnell,” said Senator Richard Blumenthal, Democrat of Connecticut.
Mr. Schumer said: “We know the fight is not over. That is for sure.” Over the next few weeks, he said, Mr. McConnell “will try to use a slush fund to buy off Republicans, cut back-room deals, to try and get this thing done.”
At least four Republican senators — Ms. Collins, Dean Heller of Nevada, Ron Johnson of Wisconsin and Rand Paul of Kentucky — had said they would vote against the motion to begin debate, enough to ensure it would fail. Other Republicans also appeared reluctant about moving forward with the bill.
“I’m just grateful leadership decided, let’s take our time, give this more thought and try and get this right,” said Mr. Johnson, who had been critical of the desire by Republican leaders to hold a vote this week.
After Mr. McConnell’s announcement, three other Republicans announced their opposition to the bill in its current form: Jerry Moran of Kansas, Shelley Moore Capito of West Virginia and Rob Portman of Ohio.
Ms. Capito and Mr. Portman, who announced their opposition together, expressed concern about how the bill would affect Medicaid and the opioid crisis, which has had devastating effects in their states.
The release of a Congressional Budget Office evaluation on Monday made it much more difficult for party leaders to win over hesitant Republican members. The budget office said the Senate bill would leave 22 million more people uninsured after 10 years, and many people buying insurance on the individual market would have skimpier coverage and higher out-of-pocket costs.
The Senate Democratic whip, Richard J. Durbin of Illinois, said the report by the Congressional Budget Office “did more to strike a dagger to the heart of this Republican repeal than anything else.”
In 2026, the budget office said, 15 million fewer people would have Medicaid coverage under the Senate bill than under the Affordable Care Act, and seven million fewer people would have coverage they purchased on their own. Faced with deep cuts in Medicaid, the report said, state officials would face unpalatable choices: restrict eligibility, eliminate services, reduce payments to health care providers and health plans, or spend more of their own money.
Appearing in Washington, Gov. John R. Kasich of Ohio cited the 22 million projection and expressed bewilderment that fellow Republicans would be on board with the bill.
“And they think that’s great?” he asked. “That’s good public policy? What, are you kidding me?”
Doctors, hospitals and other health care provider groups have come out strongly against the Senate bill, as have patient advocacy groups like the American Heart Association. But business groups were ramping up their support. In a letter on Tuesday, the U.S. Chamber of Commerce urged senators to vote for the bill.
The Senate bill “will repeal the most egregious taxes and mandates” of the Affordable Care Act, allowing employers to create more jobs, said Jack Howard, a senior vice president of the group. The bill, he noted, would repeal a tax on medical devices and eliminate penalties on large employers that do not offer coverage to employees.
A separate letter expressing general support for the Senate’s efforts was sent by a coalition of business and employer groups including the National Association of Home Builders, the National Restaurant Association and the National Retail Federation.
But Senate conservatives found themselves squeezed between business sentiment and their conservative base. The Club for Growth, a conservative group, came out against the Senate measure on Tuesday. The organization’s president, David McIntosh, noted that congressional Republicans had “promised to repeal every word” of the Affordable Care Act.
“Only in Washington does repeal translate to restore,” he said. “Because that’s exactly what the Senate G.O.P. health care bill does: It restores Obamacare.”
Vote Delayed as G.O.P. Struggles to Marshal Support for Health Care Bill