Senate Majority Leader Mitch McConnell’s plan to pass a massive overhaul of the U.S. health insurance system that has virtually no support outside of Congress and the White House became even more difficult after the release of a damaging analysis of the legislation from the nonpartisan Congressional Budget Office.

And now, with several Republican members voicing opposition to the current proposal, even a vote on a procedural motion to start consideration of the legislation appears destined to fail.

This was not the way the process was supposed to unfold. McConnell, a Kentucky Republican with a famed reputation as a legislative strategist, was expected to have the tactical prowess needed to navigate a slim GOP margin and pass a bill to fulfill the party’s seven-year promise to gut the 2010 health care law.

But he will have no one to blame but himself should the effort fail.

The majority leader has spent the last month crafting a bill in secret, keeping even his closest confidants in the dark about what the final policy would look like. And despite repeated claims that the chamber would be under no specific timeline to advance the legislation, McConnell has plowed forward with an aggressive plan to try to wrap up the Senate’s work on the health care overhaul by the July Fourth recess.

Republican rumblings

But many of his Republican colleagues are tapping the brakes.

“I have a hard time believing I’ll have the information I will need to want to support a motion to proceed on this,” Sen. Ron Johnson of Wisconsin told reporters Monday. “If Leader McConnell says failure is not an option, don’t set yourself up for failure.”

Johnson is just one in a growing faction of GOP senators who are threatening to withhold their support on the vote just to proceed to the measure. That vote would kick off an expected 20 hours of debate on the bill and tee up a vote on the final legislation by the end of this week.

“I’m a ‘no’ on it unless the bill changes,” Sen. Rand Paul of Kentucky said. “I’m not the only ‘no’ on it. I don’t think they have enough to proceed right now.”

Sens. Susan Collins of Maine and Dean Heller of Nevada are also opposed to the motion to proceed. Three defections would be enough to prevent the process from starting.

Some in GOP leadership hope their colleagues will move the process along, saying the real horse-trading could take place after the underlying measure is pending on the floor.

“It allows us to get on the bill, so, you know, I hope that’s not the case. I think it’s important for us to at least get on the bill and then … through the amendment process, have an opportunity to try and improve it in the direction that they want to go,” Senate Republican Conference Chairman John Thune of South Dakota said.

To his credit, McConnell has some room to try to bring on members who might be on the fence. He could, for example, include more money for opioid treatment in a nod to members such as Sens. Rob Portman of Ohio and Shelley Moore Capito of West Virginia.

But whether those types of side deals — which the GOP famously criticized the Democrats for pursuing when passing the initial health care law — are enough remains to be seen.

Amid the backlash from the Republican conference, McConnell is also facing growing opposition from outside Capitol Hill. Democrats, Republican governors, doctors, hospitals, health insurers and others are all rising in resistance to the legislation that would rework the law’s current tax credit structure and significantly restrict federal funding to Medicaid over the next several years.

“We sincerely hope that the Senate will take this opportunity to change the course of the current debate and work to fix problems with the current system,” the American Medical Association wrote in a letter sent Monday to McConnell and Senate Minority Leader Charles E. Schumer. “We believe that Congress should be working to increase the number of Americans with access to quality, affordable health insurance instead of pursuing policies that have the opposite effect.”

Unhelpful news

Providing ammunition to the opposition, the nonpartisan Congressional Budget Office on Monday estimated that, under the GOP proposal, there would be 22 million more uninsured individuals over the next decade than under the current law’s trajectory. The report also said health insurance costs would rise in 2018 and 2019 under the Republican plan, undercutting a major talking point for the GOP.

“We still have work to do on the bill to lower premiums,” Sen. Ted Cruz, R-Texas, said when asked whether he would vote for a motion to proceed.

Cruz is hoping to add an amendment to the bill that would give states more freedom in the type of insurance plans they offer, a stark difference from the current law that requires insurers to cover a minimum set of medical categories.

Such a measure could repel moderates, who have fought to maintain protections for patients with pre-existing conditions in the bill. It could also run afoul of chamber rules.

Senate Budget Chairman Michael B. Enzi told reporters that work has been ongoing for several weeks on addressing regulation concerns raised by senators like Cruz.

“It’s not easy. Some of the things can’t be done,” the Wyoming Republican said when asked about the possibility of such provisions complying with the reconciliation process, which the GOP is using to advance the health care measure.

Enzi repeatedly stressed the limitations imposed by the Congressional Budget Act and the Byrd Rule.

Still, despite the growing opposition from rank-and-file members, some of McConnell’s closest allies remain supportive and engaged in the process.

“Our plan will help address Obamacare’s ballooning costs for consumers by lowering premiums over time and cutting taxes,” Senate Majority Whip John Cornyn of Texas said in a statement following the release of the CBO report. “I look forward to continuing to work with my colleagues this week as we get closer to finally replacing this failed law with better care at a cost that Texans will be able to afford.”

Niels Lesniewski and Kerry Young contributed to this story.