In a legislative body that prides itself on taking its own sweet time, that is unlikely to happen soon.

“The Senate will now finish work on our bill, but will take the time to get it right,” said Senator Lamar Alexander of Tennessee, the chairman of the Health, Education, Labor, and Pensions Committee. The Washington Examiner reported Thursday that a group of 12 senators is now working on a legislative proposal, though according to Senator John Cornyn of Texas there is “no timetable” for finishing it.

Starting from scratch is not how Majority Leader Mitch McConnell envisioned an Obamacare repeal bill. The original plan was for the Senate to quickly adopt the House version once it passed in March—quick and easy. But Republican senators began criticizing the AHCA as soon as it was introduced, ensuring that even if it passed the House, it would be subject to amendment in the Senate.

Senator Rand Paul of Kentucky campaigned against the legislation from the right, denouncing the proposal as “Obamacare-lite” and rallying the House Freedom Caucus to block it from passing without changes. Along with Senators Ted Cruz of Texas and Mike Lee of Utah, Paul has pushed for a complete repeal of the current law and did not endorse the changes the Freedom Caucus won for the House bill to weaken its insurance mandates.

On the other side of the Republican caucus, more moderate senators like Senators Susan Collins of Maine and Lisa Murkowski of Alaska criticized its deep cuts to Medicaid and a provision aimed at cutting off funding to Planned Parenthood. Portman, Capito, Senator Dean Heller of Nevada and others also hammered the Medicaid sections, particularly the House bill’s provision sunsetting the expansion of the program that several Republican governors adopted. “Although I will carefully review the legislation the House passed today, at this point, there seem to be more questions than answers about its consequences,” Collins said in a statement.

McConnell has earned a reputation as a talented legislative tactician and dealmaker who has held his caucus together more effectively than Speaker Paul Ryan or his predecessor John Boehner have in the House. But his margin for error on Obamacare is razor-thin; Republicans can afford no more than two defections, meaning that some combination of staunch conservatives like Paul, Cruz, and Lee will have to endorse the same bill as Collins, Murkowski, and Heller, who is up for reelection in 2018 in a state Hillary Clinton carried in November. McConnell offered little indication about his thinking in a boilerplate statement he released on Thursday, which simply reiterated his desire to repeal and replace Obamacare.

The other obstacle Republicans face is the Senate’s complex budget reconciliation rules for passing a new health-care bill with a simple majority that is not subject to a Democratic filibuster. The bill cannot add to the deficit over the long term, nor can it make policy that goes beyond taxing and spending. House Republicans tried to write their bill in accordance with the Senate procedure, but Democrats have warned that the provisions they added to win votes in the last few weeks won’t fly. And while the House passed its measure without a final cost and impact assessment from the nonpartisan Congressional Budget Office, the Senate parliamentarian must wait for the CBO report to determine if the legislation abides by the reconciliation rules.

House Republicans celebrated their legislative feat at the White House on Thursday, reveling in a bill declared dead just weeks ago. But as the Obamacare spotlight moves to the Senate, their jubilation might end up being more than a little premature.

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