Republican leaders in the Senate are facing the same dilemma in trying to pass their Obamacare replacement bill that their counterparts in the House faced: How do you get conservatives and moderates to play nice together on health care?

That question plagued House Speaker Paul Ryan, (R-Wisc.), for weeks this spring as he and others in the GOP leadership struggled to get enough votes from members of their own caucus to pass their health-care bill.

In the end, Ryan won passage of that bill by just a single “yes” vote, with a handful of Republicans joining every Democrat in the House in voting against the bill.

But to get there, GOP leaders had to amend their bill, several times, to placate concerns by conservative and moderate members of their caucus.

Doing so was tricky, because conservatives, as a rule, favored a bill that more aggressively moved toward their goal of complete Obamacare repeal. On the other hand, moderates feared provisions that would lead to many more uninsured people, and higher premiums for millions of others.

Oftentimes, one provision that would make conservatives happier made moderates less so. And vice versa.

If anything, Senate Majority Leader Mitch McConnell‘s task is even harder in the upper chamber of Congress after unveiling a discussion draft of the Senate’s own bill Thursday.

Where Ryan could afford to lose 20 or more Republicans, the Kentucky senator McConnell can afford just two defections.

Republicans have 52 senators, and a tie vote on the new bill would have to be broken by Vice President Mike Pence, a fellow GOPer.

And right now, there are more expected “no” votes than just two after McConnell released a draft of the GOP’s Senate bill on Thursday. At the same time, McConnell has said he wants to have a vote on the bill by late next week, before Congress’ Fourth of July recess, which would avoid senators going home for several weeks to hear concerns about the bill from their constituents in person.

Robert Laszewski, president of the consulting firm Health Policy and Strategy Associates, in a client update issued Thursday, wrote that, “If McConnell and the Republicans can” win passage of the bill next week, “it will be one of the most masterful legislative jobs in recent memory as the Republican leader.”

McConnell, Laszewski wrote, will try “to thread a needle balancing the demands of conservative Republicans trying to unwind the ‘Democratic welfare state,’ and a handful of more pragmatic moderate Republicans opposed to simply throwing millions of people off their coverage.”

Hours after the 142-page bill was released, four GOP senators, Rand Paul of Kentucky, Ted Cruz of Texas, Ron Johnson of Wisconsin, and Mike Lee of Utah, gave a sense of how tight that needle is when they issued a joint statement saying “we are not ready to vote for this bill.”

That quartet of conservatives, while saying they “are open to negotiation and obtaining more information” before a vote. But they added that the draft as is does not appear like it will fulfill what they called “the most important promise that we made to Americans: to repeal Obamacare and lower their healthcare costs,” their statement said.

Cruz said later, “This current draft doesn’t get the job done.” But he added, “I think we can get to yes,” particularly if the bill can guarantee a reduction in insurance premiums.

Two moderates separately released statements of their own.

Sen. Dean Heller, (R-Nev.), said he has “serious concerns about the bill’s impact on Nevadans who depend on Medicaid.”

“I want to make sure the rug is not pulled out from Nevada or the more than 200,000 Nevadans who received insurance for the first time under Medicaid expansion,” Heller said.

Sen. Shelley Moore Capito, (R-W.Va.), in her own statement, said she will weigh whether the bill “provides access to affordable health care for West Virginians, including those on the Medicaid expansion and those struggling with drug addiction.”

Other Republican senators are likely to have concerns about both the phase out of Medicaid’s expansion under Obamacare, and about a cap on spending for Medicaid overall, both of which are called for by the bill. There also will be concerns that the bill’s restructuring of the system for subsidizing customers of individual health plans will lead to much higher costs for many older Americans, and those with health problems.

Elizabeth Carpenter, a senior vice president at Avalere Health, a health-care consultancy, said that if the Senate bill becomes law “we’re likely to see significantly more uninsured people compared to the current [Obamacare law].”

“With most of those shifts in coverage coming from the Medicaid program,” Carpenter said.

She said that without Medicaid benefits that were expanded to many more poor adults under Obamacare, people who are “at the poverty line are very unlikely to be able to afford insurance.”

Carpenter also noted that more than half of all customers who buy insurance plans from government-run Obamacare marketplace receive “cost-sharing reductions.” Those federally funded subsidies, which reduce the amount of out-of-pocket health costs low-income customers face, are set to be eliminated in 2020 under the Senate bill.

If those subsidies end, people who are heavy users of health-care services could face thousands of dollars or even more per year in new costs as a result.

All of those factors will give at least some moderates pause. And that in turn, will create pressure on McConnell and other GOP leaders to assuage their concerns.

But if they do so by watering down provisions in the bill, or by adding provisions, McConnell risks alienating conservatives even more than the bill already has done.

In his client note, Robert Laszewski noted that the Medicaid reductions proposed by the bill are big selling points to conservatives.

“The penultimate question is this,” Laszewski wrote. “Will the Medicaid rollback be enough to keep the most conservative Republican Senators onboard in the face of a truly ‘Obamacare lite’ approach to the individual market while not pushing the moderates off the bill — particularly Republican Senators from Medicaid expansion states?”

Laszewski added, referring to the entire proposed bill, that he personally could not think of “a better tactical approach to getting 50 Republican Senators onside.”

“If this isn’t enough, just what would these moderate and conservative Senators expect to get,” he wrote.