That's because Republicans are relying entirely on their own party to pass this legislation, and Senate leaders need 50 of their 52 members on board to pass a bill. (Democrats won't play ball as long as Republicans' intent is to repeal Obamacare.)
And the Republican Party is severely ideologically divided, spread between conservatives who fundamentally don't believe in the government's role in health care and moderates who think Obamacare was a step in the right direction.
Since the bill was negotiated in secret and revealed three weeks ago, it has been losing support, not gaining it.
These next few weeks are it's make-or-break time for the Senate bill. Here are four possible scenarios that would derail it:
Scenario one: The anti-Obamacare purists draw a line on preexisting conditions
We already know that at least four conservatives don't think the current bill does enough to repeal Obamacare. (Large parts of the law will still be intact.) So Sen. Ted Cruz (R-Tex.) came up with an idea during the break: Lift all Obamacare regulations from insurers as long as they sell one plan that covers people with preexisting conditions and provides prenatal care, etc.
The Post's Paige Cunningham explains in her daily health-care newsletter that Cruz's idea would essentially divide the health insurance market into two:
1) Plans for healthy people, who would buy cheaper but skimpier plans.
2) Plans for sick people, who would have no choice but to buy the one that covers their illness. This would likely send prices for the bill so high they might not be able to afford insurance. Health-care experts say it could also cause premiums for everyone else to rise as healthy people forgo insurance.
And that's likely a non-starter for more moderate senators. “They'd have their name on something that was worse than what they're saying Obamacare is,” in terms of premiums rising, said Alice Rivlin of the Brookings Institution.
GOP senators to watch: Cruz, Mike Lee (Utah) and Ron Johnson (Wis.). support this change. But powerful senators like Sen. Charles E. Grassley (Iowa), who chairs a key finance committee, says this idea amounts to “subterfuge to get around preexisting conditions” and “I would object to that.”
Scenario two: Moderate senators just can't agree to cut off Medicaid
Republican senators who represent some of the 30-plus states that expanded Medicaid under Obamacare are increasingly acknowledging that millions of lower-income people got health insurance that way. And it would be politically unfeasible to take it away, like the Senate bill now proposes. (It would dramatically cut Medicaid by an estimated $800 billion by 2026.)
Not helping compromise: Republican governors, like those in Ohio and Nevada who expanded Medicaid, have said the Senate version needs to keep that expansion intact.
GOP senators to watch: This is probably the largest bloc of opposition. It includes Dean Heller of Nevada, the most vulnerable GOP senator up for reelection in 2018. Rob Portman (Ohio), Shelley Moore Capito (W.Va.), Lisa Murkowski (Alaska), and Cory Gardner (Colo.).
Scenario three: At least three senators who have state-specific issues draw a line
At least two GOP senators have consistently said they want this health-care bill to include federal funding for women's nonprofit health-care clinics, like Planned Parenthood. The Senate bill as it stands now doesn't.
A handful of senators want to make sure that the Senate boosts addiction treatment for the growing opioid crisis. (Senate leaders are considering adding $45 billion, though some senators say that's not enough.)
There are nearly half a dozen state-specific problems that could sink the bill by being non-starters among senators whose first jobs are to represent their own states. Remember: Senate leaders can only afford two defections.
GOP senators to watch for: Murkowski and Susan Collins (Maine) have drawn a line on Planned Parenthood funding. Portman and Moore Capito are leading the way on the opioid funding conversation.
Scenario four: The bill stays unpopular
The GOP bill right now is political kryptonite, says The Fix's Aaron Blake: “Support for the bill is languishing between just 1 out of every 8 Americans and 1 out of every 6 Americans.”
Not helping: An estimate in June by the nonpartisan Congressional Budget Office that the Senate's bill would cause 22 million more people to lose insurance over the next decade, raise premiums for lower-income elderly people by 280 percent, and cut taxes for the wealthy.
Watch for: Pretty much everyone but all the bill's hardcore supporters. “Some senators must realize this is a very unpopular bill, and they'd be better off politically it if went down,” Rivlin said.
One scenario for how the bill could pass
Democrats. If Senate Majority Leader Mitch McConnell (R-Ky.) can’t get a consensus with his side, he’s threatened to rewrite the bill to make it tenable for Democrats. That would mean Republicans could lose the 10 or so moderates and conservatives in their caucus and still pass a health-care bill — one that would keep large parts of Obamacare intact.