Senate Republicans have just days to pass a bill that would repeal major chunks of the Affordable Care Act, scale back federal spending on health care and dramatically change health insurance in the United States.

But they don’t know exactly how it will work.

Named for cosponsors Sens. Lindsey Graham and Bill Cassidy, the Graham-Cassidy bill will not be scored by the nonpartisan Congressional Budget Office before the Senate faces an end-of-month deadline to pass it by a simple majority.

While the broad outlines of the bill are known, that means senators will have to make a decision to vote for or against the bill without knowing how many millions of Americans could lose insurance, how much money their state could gain or lose under it and what effects it might have on insurance premiums, according to their own scorekeeper.

Outside groups have made their own estimates, all of which say the bill will lead to millions fewer Americans having insurance. A recent report from the Center on Budget and Policy Priorities wagers that more than 32 million people could lose healthcare as a result of Graham-Cassidy, which could slash federal healthcare funding by nearly $300 billion over the next decade.

But for some Republicans, the details of the bill are not as important as the years-long promise they made to repeal Obamacare.

“You know, I could maybe give you 10 reasons why this bill shouldn’t be considered,” said Republican Sen. Chuck Grassley of Iowa. “But Republicans campaigned on this so often that you have a responsibility to carry out what you said in the campaign. That’s pretty much as much of a reason as the substance of the bill.”

Republican Sen. Pat Roberts of Kansas told Vox that the bill needed to be passed regardless of imperfections because of the problems of the Affordable Care Act.

“Look, we’re in the back seat of a convertible being driven by Thelma and Louise, and we’re headed toward the canyon,” he said. “That’s a movie that you’ve probably never seen. So we have to get out of the car, and you have to have a car to get into, and this is the only car there is.”

When the Affordable Care Act was being considered in 2010, then-Speaker Nancy Pelosi famously said that lawmakers would have to “pass the bill so that you can find out what is in it.” She meant that the “fog of controversy” over the famously tortuous legislative process behind the bill had clouded the actual benefits in it, but the quote was seized on by many conservatives over the years to criticize the Democratic law.

But the Affordable Care Act was debated after a rigorous congressional schedule that included hearings before multiple committees, changes to the bill designed to win Republican support and a painful month for Democrats of angry constituents arguing against the bill at town-hall meetings.

The Graham-Cassidy bill, by contrast, is the result of fast-tracked and largely backroom conversations between Senate Republicans. There will only be one day of Senate hearings on the bill next week. At a press conference this week, Senate Minority Leader denounced it as “a hastily constructed piece of legislation put together in back rooms by only one party.”

“It’s quite unprecedented, and it’s very, very bad process on a lot of levels,” Alice Rivlin, the founding director of the Congressional Budget Office, director of the Office Management and Budget under the Clinton Administration and a senior fellow at the Brookings Institution, told TIME. “To pass a major healthcare bill with the votes of only one party is a big mistake. They should wait for the CBO score. It’s bad PR, and it’s bad politics.”

The major impetus for the current push is a deadline to use a process known as reconciliation, which requires just a simple majority of 50 votes (with Vice President Mike Pence breaking the tie) to pass a bill. Earlier this month, the Senate parliamentarian set Sept. 30 as the deadline.

But earlier this week, the CBO issued a statement saying that it would only provide a “preliminary assessment” of Graham-Cassidy’s impact before the end of the month. Specific estimates of the bill’s impact on the deficit, the number of insured Americans, and the cost of insurance premiums would take “at least several weeks.”

“I would say it’s either never happened or it’s extraordinarily unusual for legislation to be considered without a full CBO score, particularly under reconciliation,” Frederick Isasi, executive director of Families USA, the nonprofit health advocacy organization, tells TIME. “Many Republicans pride themselves on being fiscally conservative, so it’s difficult to understand how they would be comfortable voting on sweeping legislation that will impact at least 90 million Americans without a full accounting from the CBO of all financial and coverage impacts.”

This hasn’t stopped Senate Republicans from moving ahead. Senate Majority Leader Mitch McConnell intends to “consider Graham-Cassidy on the floor next week,” his spokesman David Popp confirmed to TIME on Wednesday. When asked about the lack of a CBO score at a press conference, Senator Graham, the bill’s eponymous co-sponsor, deflected, saying only that “the CBO has told us that they’ll have a score for us, and it’ll be on the cash aspect of it, so we’ll have a chance to look at that.”

But it may yet stop the bill. Republicans can afford only two defections in the Senate to keep the bill from failing, and Sen. Rand Paul of Kentucky has already made it clear that he won’t vote for Graham-Cassidy. Three Republicans who voted against the last repeal attempt remain on the fence: Sens. John McCain of Arizona, Susan Collins of Maine and Lisa Murkowski of Alaska.

In his dramatic late-night speech against that attempt, McCain complained that the bill wasn’t going through the regular legislative process, and Collins has raised similar concerns this time around about Graham-Cassidy.

“I am still looking at it, but I have major reservations,” Collins told reporters this week. “We don’t have a CBO score.”

Get our Politics Newsletter. The headlines out of Washington never seem to slow. Subscribe to The D.C. Brief to make sense of what matters most. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Contact us at letters@time.com.