Senate Republican leaders are postponing a vote on their bill to repeal and replace Obamacare after a critical mass of senators said they would block the bill as written.

Senate Majority Leader Mitch McConnell had been pushing for a vote by the end of the week, and he could only lose two votes. But by Tuesday afternoon, at least five Republican senators said they would not support a procedural vote to start debate on the bill as currently written — enough to stop it.

“We’re going to continue the discussions within our conference on the differences that we have,” McConnell said at a press conference Tuesday afternoon. “We’re going to continue to try and litigate — consequently we will not be on the bill this week, but we’re still working toward getting at least 50 people in a comfortable place.”

Sens. Susan Collins of Maine, Dean Heller of Nevada, and Rand Paul of Kentucky — two moderates and a conservative — said on Monday night that right now they would block debate from starting on the bill. Conservative senators Mike Lee and Ron Johnson soon joined them.

Senate Republicans are expected to continue their debate on the health care bill after the July 4 holiday. “We're not going to vote this week, so we have more time to work on it until we get it done,” Sen. John Cornyn said Tuesday afternoon.

Conservative opposition to the plan is hardening, because they don’t believe it does enough to repeal Obamacare. Meanwhile, several moderates have expressed doubt, which would also sink the plan, especially now that the Congressional Budget Office projected Monday that 22 million fewer Americans would have health insurance under the plan.

There are still about 35 Republican senators who will vote for the bill no matter what. But the others will be the difference between failure and passage.

“You’re not gonna get 49. You’re either gonna get 50 or probably 35,” Sen. Lindsey Graham (R-SC) told reporters Monday, adding that the CBO estimates “are going to make it harder to get to 50, not easier.”

After this week’s setback, McConnell will have to regroup and figure out whether he can tinker with the Senate bill next month to get 50 votes — or if Republicans will fall short in their quest to repeal Obamacare.

The Senate’s path to passing a health care bill is narrow

McConnell started with a narrow margin of error: 50 of the 52 Senate Republicans must support the bill, under the procedural shortcut Republicans are using to pass the plan with a bare majority of 50 and avoid a Democratic filibuster.

Conservatives have begun to revolt, and moderates are blanching at the plan’s projected coverage losses. The majority leader has some room to negotiate; he has about $200 billion to play with, according to the CBO. But any money he pumps into the bill to hold on to moderates could drive away conservatives. Likewise, moving the bill any further to the right — and potentially increasing that 22 million more uninsured estimate — could fortify moderate opposition.

About three dozen Republican senators would probably vote for any bill that McConnell put forward. They’re party people. But shoring up those last 15 or so votes is the trick.

Many congressional aides and lobbyists believe McConnell is pushing forward for a vote regardless of whether it would fail. He surely wants to pass a bill to repeal Obamacare, fulfilling a seven-year pledge that propelled him to power, but the effort has proved more difficult than Republicans expected.

Conservatives are hardening their opposition to the Senate bill

A quarter of conservative senators — Rand Paul, Mike Lee, Ted Cruz, and Ron Johnson — announced their opposition to the bill last week. They’re holding firm.

Paul told reporters Monday that he would vote to block even a procedural vote to start debate on the legislation.

“Of the current bill, yes,” Paul said when asked by reporters if he’d oppose that procedural vote. “Absolutely.”

Cruz told reporters that “significant work remains to be done” and argued that the plan didn’t do enough to lower premiums. The CBO projected that premiums would eventually go down under the plan, but many Americans would have to pay higher out-of-pocket costs for their health care.

Johnson told me he wanted to repeal the entire law, returning the health insurance market to what it was like before Obamacare. The current Senate bill keeps much of Obamacare’s infrastructure on the private insurance side, though it gives states more leeway to roll its regulations back and scales back the financial aid available to low- and middle-income Americans. The bill also ends Obamacare’s Medicaid expansion and places a federal spending cap on the entire Medicaid program.

“I would recommend people go back to what were the conditions prior to Obamacare, embrace those conditions, embrace free markets,” Johnson said. “Get rid of the mandates that have artificially driven up the costs of insurance. We can do this ... and solve the problem of preexisting conditions using high-risk models."

But that is almost certainly a nonstarter for a dozen or more Senate Republicans. Obamacare’s protections for people with preexisting conditions, particularly the requirement that health plans cover every American no matter their health status, are overwhelmingly popular.

Moderates are also starting to defect from the Senate plan

But McConnell has problems on the other ideological end of his conference, too.

Sen. Dean Heller (R-NV), a swing vote in a swing state who faces the toughest reelection race of any Republican next year, said Friday he would oppose the bill. He was joined by Nevada’s exceedingly popular Republican governor, Brian Sandoval, who has also spoken out against the Senate plan for its Medicaid cuts.

“In this form, I will not support it,” Heller said, adding that he would also vote against the procedural motion to start debate on the bill. “It’s going to be very difficult to get me to a yes.”

Then on Monday evening, after the CBO report projected 22 million fewer Americans would have insurance under the Senate bill, Sen. Susan Collins (R-ME), another crucial moderate vote, said she would oppose the bill and the motion to start debate.

I want to work w/ my GOP & Dem colleagues to fix the flaws in ACA. CBO analysis shows Senate bill won't do it. I will vote no on mtp. 1/3 — Sen. Susan Collins (@SenatorCollins) June 26, 2017

Collins, Heller, and Paul made a trio that was enough to block debate from starting on the legislation — and more senators had strong reservations about the bill.

Several other moderate senators — Rob Portman of Ohio and Shelley Moore Capito of West Virginia — have fretted over the bill’s Medicaid cuts, and the CBO projected that the current Senate bill would reduce the program’s spending by $772 billion over 10 years, versus current law.

Another, Sen. Bill Cassidy of Louisiana, demurred when asked whether he could support that procedural vote. He said he still needed time to understand the CBO report.

“You’d like to have questions answered before you proceed,” he said. Asked directly if he’d vote against the motion, Cassidy replied: “Can you talk to me tomorrow? Because I actually have not even considered that.”

McConnell still has room to maneuver, so it’s not over yet

But even if things are looking grim for the Senate health care bill right now, that doesn’t mean it’s game over yet.

“You don't want to bring something up unless you know you have the votes to pass it, but I also think we may not know if we have the votes to pass it until we bring it up,” Sen. John Thune, the No. 3 Republican, told reporters Monday.

The complex Senate rules that Republicans are using to pass their bill with only 50 votes actually give McConnell some new wiggle room based on the CBO score: He can add as much as $200 billion to the bill and still meet the budget targets that the rules require.

It’s not clear if more money is enough to bridge the ideological gaps that have divided Republicans. McConnell could shovel more money toward the opioid crisis, to help win over Portman and Capito. He could give Collins and Sen. Lisa Murkowski (R-AK), another moderate swing vote, a chance to remove Planned Parenthood defunding from the bill. He may bet on the goodwill of conservative senators who would rather vote for an imperfect bill than block Obamacare repeal.

It might not be enough.

“Health care was broken before Obamacare. Obamacare made it worse, and I don’t think we’re necessarily doing anything to fix the problem,” Paul said. “This is why it’s worse to pass a bad bill than it is to pass no bill.”

But even Paul, perhaps the most strident opponent of the bill right now, hinted at a path forward.

“You don’t have 50, you don’t have 52 for what’s in the bill now. How do you get there? You make the bill narrower,” he said. “Then maybe you pick up one. Then you make it narrower and narrower. So it’s not making the bill bigger; it’s actually making the bill more like a repeal bill.”

Tara Golshan contributed reporting.