Senate Republican leaders are threatening to put their health care bill on the floor next week and dare their members to oppose it. It will be time for the dozen or so holdouts to walk the walk after talking the talk against the plan for the past few weeks.

Rand Paul, for one, sounds ready to back his words up and vote against it. If he does, the Republican effort to repeal and replace Obamacare will be in serious trouble.

Paul has been one of the most outspoken opponents of the Senate legislation for weeks now. He argues it doesn’t do enough to unwind Obamacare and it funnels federal funding to insurance companies, creating what he has called a new Republican entitlement program.

Now, with Senate Majority Leader Mitch McConnell expected to release a revised plan Thursday, Paul is digging in even further. He’s shown no willingness to budge from his position and it seems almost certain that the provisions he most firmly opposes won’t be removed from the bill.

“As far as I can tell, the new bill is the same as the old bill,” the Kentucky senator told reporters on a conference call Wednesday. “I can’t support it.”

Senate Republican leaders really might need Paul to pass the bill

Three Senate Republicans can kill the bill. Two moderates — Susan Collins of Maine and Dean Heller of Nevada — seem pretty hardened in their opposition. (As many as a dozen Republican senators say they oppose the current bill, but GOP lobbyists, and likely Senate leadership, privately believe some of them would ultimately cave when the time comes.)

Collins, who is weighing a gubernatorial bid next year, is asking for a complete overhaul. Heller tied himself to his overwhelmingly popular Republican governor, Brian Sandoval, who has been one of the most vicious critics of the bill from within the GOP. He faces the toughest reelection race of any Senate Republican in 2018.

That makes Paul, who opposes the bill from the right, an essential vote. He’s been even more outspoken against the plan than conservative Sens. Mike Lee (R-UT) and Ted Cruz (R-TX). Those two seem narrowly focused on rolling back more of Obamacare’s insurance regulations. Paul wants that too, but he is also opposed to keeping some of the health care law’s taxes.

Then there is Paul’s strongest objection: the stabilization funding for health insurers. The Republican bill currently includes $50 billion to stabilize the Obamacare insurance markets in the next few years, before the GOP bill’s major provisions take effect, paid to health insurers to cover high-cost patients. The current plan also provides $62 billion for longer-term state stabilization programs to reduce health care costs for vulnerable populations, and it authorizes Obamacare subsidies paid to insurers to lower out-of-pocket costs for lower-income Americans.

The stabilization funding is popular among the more mainstream Senate Republicans and likely to remain in the bill. It could even be increased, if McConnell believes more money will help reduce the projected coverage losses — 22 million fewer Americans with health insurance in 2026, versus Obamacare, per the Congressional Budget Office — under the current bill.

So Paul, paired with Collins and Heller, could stop the legislation. He’s been sticking his neck out further and further: On Wednesday, the day before the new bill is to be unveiled, he wrote an op-ed for Breitbart trashing the GOP plan and held a conference call with reporters to slam it again.

I asked him on Wednesday if he was willing to be one of three Republican votes to kill the plan. He sounded like he was.

“I ran on repealing Obamacare. If it doesn’t repeal Obamacare and it creates a giant insurance bailout superfund, I can’t be for that,” he told me.

Paul is viciously opposed to a core provision of the GOP plan

Paul, a self-professed libertarian, has been loudly opposing the stabilization funding in the Republican bill for weeks. He told me a month ago he would oppose a bill with that kind of money directed to health insurers.

"If you told me I couldn't repeal everything and some of Obamacare would remain, I would vote for that as an imperfect bill," he said then. "But I'm not voting for one that has new Republican entitlement programs — like that stabilization fund they're talking about is a Republican entitlement program for a billion-dollar insurance industry."

He hasn’t softened at all on that position, even though most Republicans believe stabilization funding is necessary to keep the Obamacare markets functioning for a few years before they transition to a new health care system.

There have been no indications that the money will be removed in the revised bill.

“I personally believe that all of the pork that’s being added to the bill … is not a conservative notion,” Paul told reporters on the conference call, repeatedly referring to the stabilization money as an “insurance bailout superfund.”

Paul’s fixation on the insurance funding separates him from Cruz and Lee, the conservatives who he is otherwise allied with. The other two are conditioning their support on a Cruz proposal that would allow health insurers to sell non-Obamacare insurance as long as they also sold plans that complied with the health care law. The policy is currently being reviewed by the Congressional Budget Office and is expected to be included in one of the two versions of the revised Senate bill released Thursday.

But Paul actually said Wednesday that the Cruz amendment could make his problems with the Senate bill worse. The policy could drive up costs for people in the Obamacare markets, as Vox’s Sarah Kliff detailed, which the federal government would then have to step in and subsidize to prevent a death spiral.

“The impressions and the rumors that we’re hearing is that’s gonna mean a lot more money in insurance bailout fund and ultimately also mean some sort of price controls,” Paul said on the conference call, adding that was “foreign to any notion of capitalism.”

Paul’s solution, if next week’s vote fails, is to scrap any replacement provisions and focus on the parts of Obamacare that Republicans can agree to repeal. Even Collins, for example, has said some taxes on the health care industry should be scrapped because they drive up the cost of health insurance.

“I guarantee that, on repeal, Susan Collins and I have common ground,” Paul said.

Then, the other Senate Republicans could work with Democrats on a different bill with other policies, like stabilization funding, that Paul opposes. The senator left it to his GOP colleagues to pass “big government spending priorities” with Democratic votes.

“Conservatives won’t come onboard, or at least this conservative won’t, if the bill includes an insurance bailout superfund,” Paul said on his conference call.

That promise will be put to the test soon.