12 GOP senators have criticized Paul Ryan’s health care bill. 3 defections kill it.

Speaker Paul Ryan may be celebrating the Congressional Budget Office’s analysis of his American Health Care Act, but reactions from Republicans in the Senate suggest that the bill is unlikely to ever become law — at least in its current form.

Within hours of the CBO score’s release, multiple Republican senators acknowledged its damning implications for Ryan’s bill. And this wasn’t just Republicans from swing states: Reasonably party-line voters Sen. John McCain (R-AZ) and Sen. Bill Cassidy (R-LA) joined the pile-on. (The CBO is the nonpartisan scoring agency that crunches the numbers on how much proposed congressional legislation would cost.)

Republicans control 52 seats in the Senate, so they can afford just three defections and still pass the bill through the budget reconciliation process, assuming all Democrats oppose it. But at least 12 Republican senators have already objected to portions of the bill or called on the House to revise it.

That doesn’t any Republican health care overhaul is dead, of course. It just means it’s highly unlikely to pass in its current form or with only cosmetic changes. “It’s quite possible that after some political wrangling and behind-the-scenes maneuvering some of these hesitant voices could be ayes,’” says Geoffrey Skelley, a congressional analyst at the University of Virginia’s Center for Politics. “But at this point there’s almost no way to see it passing.”

Speaker Ryan and House Republicans did get AHCA through two high-profile committee hearings last week — in party-line votes with no defections — and Republicans on the Hill have expressed confidence that they’ll be able to pass the bill through the House.

But the real threat to the bill’s passage has always been the Senate — where individual members have greater power to singlehandedly torpedo a legislative push, and where Republicans tend to be accountable to a more politically diverse electorate.

Before Monday, the most serious threat to Ryan’s bill appeared to be among the senators on the Republican Party’s right flank. Arch-conservatives in both chambers openly threatened to withhold their support for the bill, arguing that it doesn’t go far enough toward dismantling Obamacare. The CBO found that AHCA would bring down the federal deficit by $447 billion — something that may assuage the doubts of the far-right Freedom Caucus, Skelley says.

“Considering the budget deficit number, it’s possible conservatives have the ammunition to shore up their right flank with those who haven’t expressed much love for the replacement plan so far,” Skelley said.

But it’s certainly far from clear that will be enough to win over the three most prominent right-wing critics of AHCA — Sen. Rand Paul (R-KY), Sen. Mike Lee (R-TX), and Sen. Ted Cruz (R-TX). On Monday, before the CBO score’s release, Paul again reiterated to reporters that he wanted a “clean repeal” of Obamacare that would do away with it almost in its entirety.

And even if Cruz, Paul, and Lee come on board eventually, there probably still aren’t 51 Republicans who support the bill.

Skelley thinks the Democrats may have the best luck picking off Sen. Dean Heller (R-NV). There are several reasons Heller looks like a good bet to oppose Ryan’s bill: He’s from a state Hillary Clinton won; he’s up for reelection in 2018; a Republican lost a Senate race in Nevada this fall; and more than 300,000 people in Heller’s state receive coverage through the ACA.

Indeed, Politico obtained audio published on Monday showing Heller raising “numerous objections” to Ryan’s bill before the CBO score came out.

Beyond that, Democrats will probably look to lobby four Republican senators — Rob Portman of Ohio, Shelley Moore Capito of West Virginia, Cory Gardner of Colorado, and Lisa Murkowski of Alaska — who criticized Ryan’s bill when an early draft of it surfaced weeks ago.

The four sent a letter arguing that a draft of Ryan’s bill did not “adequately protect” Medicaid; Ryan’s bill wound up including steep cuts to the program. (The CBO says AHCA would cut Medicaid spending by $880 billion over the next decade, according to Vox’s Sarah Kliff.)

The AHCA would also change how the federal government gives people tax credits to afford insurance. Tax credits would be based on age rather than income, and they wouldn’t be adjusted based on the cost of insurance premiums in different locations. Alaska, Murkowski’s state, stands to lose the most under these changes.

Moreover, Sen. Tom Cotton (R-AK) has also repeatedly criticized the bill, saying on ABC this weekend that it “would have adverse consequences for millions of Americans.”

And Sen. Susan Collins (R-ME), who crosses the aisle more frequently with her votes than most, has said she doesn’t think the bill should be linked to funding for Planned Parenthood. (She and Sen. Cassidy have released their own replacement plan.) Collins reacted to the CBO score by calling it a “cause for alarm that many people would lose coverage,” according to Bloomberg’s Sahil Kapur.

That makes at least 12 Republican senators who suggested they might break ranks, and confirms that the CBO is very bad news for Ryan’s bill. “The fact that so many people stand to lose their insurance is likely to make Republican moderates more skittish. That’s the new dynamic this brings,” Skelley said.

Here’s a list of all of the Senate Republicans who have criticized the Ryan bill or called for it to be revised:

Update: A previous version of this story contained a Tweet from a reporter that misquoted Sen. Purdue as calling on the House to “slow down” its healthcare bill. The Tweet has been removed from this story.