The clock on Obamacare repeal runs out in 12 days, and Republican senators are using that deadline to ready one last shot at the health care law.

Sens. Bill Cassidy (R-LA) and Lindsey Graham (R-SC) have put together the GOP’s last-ditch plan to overhaul the Affordable Care Act: a bill that would take Obamacare’s funding and turn it into a block grant, while also overhauling Medicaid and rolling back some of the law’s protections for people with preexisting conditions.

Time and politics are against them, but there have been signs of momentum in recent days. Senate leaders and the White House are reportedly preparing for the possibility of putting Cassidy-Graham on the Senate floor by September 30, the deadline for Senate Republicans to pass a repeal bill using “budget reconciliation,” which allows the bill to advance without any Democratic votes.

A lot needs to happen in less than two weeks for this gambit to succeed, not least of which is finding 50 votes in the Senate to pass Cassidy-Graham (Vice President Mike Pence could cast the tie-breaking vote), which no other Obamacare repeal bill put forward by Republicans this year has managed to do.

But the signs can no longer be ignored. After being dismissed as a joke for most of the past two months, Cassidy-Graham has forced Washington to take it seriously, no doubt aided by the September 30 deadline and the expiring dream of Obamacare repeal. Lobbyists who had long ignored the plan say they now take it seriously. Senate leadership, which had downplayed the bill’s odds, is starting to buy in.

What we know for sure is the final two weeks of September promise at least one last act for Obamacare repeal. Whether it will actually happen is far from certain. But any Obamacare repeal bill will start with upward of 40 votes in the Senate, and that thin margin gives Cassidy-Graham a chance if a few swing votes break their way.

“I am pretty confident that we’re gonna get there on the Republican side,” Cassidy told reporters Friday, feeding the perception that they are nearing a majority.

Here’s what would need to happen for this long-shot legislation to beat the odds and succeed.

1) It clears the procedural hurdles to getting on the Senate floor

Cassidy-Graham (which is also sponsored by Sens. Dean Heller of Nevada and Ron Johnson of Wisconsin) has been floating around for months, but the final text was not released until last week.

If they want to get it on the Senate floor by September 30, there are a few purely mechanical steps that need to be taken:

The Congressional Budget Office needs to complete its analysis of the bill.

The Senate parliamentarian needs to assess whether the plan complies with the chamber’s “budget reconciliation” rules.

The second step can’t happen without the first, because the parliamentarian uses the CBO score in part to assess whether provisions in the bill meet the standards of the Byrd Rule, which require any bill considered under budget reconciliation to directly affect federal spending or revenue. Outside budget experts have questioned whether some provisions in the bill would meet the Byrd Rule’s requirements.

It is notable then that, according to Politico, Senate Majority Leader Mitch McConnell has asked the CBO to prioritize scoring the bill.

2) Senate leaders and the White House buy in all the way

Cassidy-Graham has snuck up on most of Washington in part because Senate leadership and the White House have largely kept their distance and kept mum.

When the bill was released, President Trump put out a tepid statement: “As I have continued to say, inaction is not an option, and I sincerely hope that Senators Graham and Cassidy have found a way to address the Obamacare crisis.”

Even as he assailed a Democratic single-payer bill on Twitter, the president didn’t take the opportunity to promote the last Republican bill standing.

McConnell, for his part, seems allergic to any risk of another repeal humiliation, after Senate Republicans tried and failed to pass three different repeal bills in late July. He has told Cassidy and Graham that they would need to find the votes for their bill on their own, and his No. 2, Sen. John Cornyn (R-TX), said just 11 days ago that the bill had no real hope of getting a vote.

“McConnell has zero interest in presiding over another goat rodeo,” one health care lobbyist told me in recent days.

But at some point, the White House and Senate leaders would need to be fully invested if they were going to bring the bill to the floor. Politico reported over the weekend that McConnell is warming up to the idea, given the positive reception to the bill in his conference.

In the end, the majority leader will make the call. Leadership is expected to take a more formal whip count this week. Based on my conversations with lobbyists and the reporting of other outlets, McConnell will have to be absolutely sure that the bill has 50 votes before he puts it on the floor.

After the failures of July, McConnell is going to own the outcome of a vote on Graham-Cassidy one way or the other.

3) No Republican senators bolt from the bill

Senate Republicans have already shown it’s easy to get 45 or so votes for an Obamacare repeal bill. So-called “skinny” repeal — the last plan that the Senate voted on in late July — got 49.

So the first step to 50 for Cassidy-Graham is not losing any unexpected votes. That could theoretically be a challenge. Under the bill’s block grant formula, there will be some clear winners and losers among the states. Based on an early analysis from the left-leaning Center on Budget Policy and Priorities, states like Ohio, West Virginia, and Arizona — all represented by Republican senators who have at times expressed some apprehension about the various repeal plans — would lose hundreds of millions, or even billions, of dollars under the block grant.

More state-by-state analyses will be released in the coming days. Cassidy’s office is producing its own numbers, in hopes of assuaging any jittery senators.

“I’m trying to get the numbers for West Virginia,” Sen. Shelley Moore Capito (R-WV), one of those potential swing votes, told me Thursday. She did add of the bill: “I think the flexibility piece is something that’s very attractive.”

The path to 50 — remember there are only 52 Republican senators, so Cassidy and Graham can only lose two of their own members — starts with not losing any unexpected votes. They haven’t so far, but it will be something to watch closely as expert analyses roll in and senators start to hear back from their states.

As long as they hold on to senators like Capito and Ohio’s Rob Portman, who represent states that could see funding cuts under Cassidy-Graham, the bill should be within striking distance of a majority.

4) Some swing votes break in favor of the plan

Assuming there are no surprise “no” votes, the legislation must still pick up a few votes to get to 50. There are four senators in particular whose votes seem most in doubt:

Sen. Susan Collins (R-ME)

Sen. Lisa Murkowski (R-AK)

Sen. Rand Paul (R-KY)

Sen. John McCain (R-AZ)

Cassidy-Graham must win two of those four — and not lose any others — to get a majority and pass the Senate.

McCain famously cast the decisive vote to strike down “skinny” repeal in late July, saying at the time that Republicans shouldn’t ram through a partisan bill but should instead produce a bipartisan plan through regular order.

Nevertheless, he seems the most likely to flip. Graham is his closest friend in the Senate, and McCain has said some positive things about the bill’s concept. If Arizona Gov. Doug Ducey, whom McCain has deferred to throughout the debate, endorses the bill, that might be enough justification for the senator to come around.

On the other hand, McCain seemed to reiterate Sunday that he would prefer a bipartisan health care bill that is produced in committee hearings — Cassidy-Graham meets neither of those tests.

John McCain backs the bipartisan work on Obamacare fixes by Alexander and Murray. Pretty clear signal.https://t.co/dWU6Guvntw — Sahil Kapur (@sahilkapur) September 17, 2017

(Johnson, who chairs the Armed Service and Government Committee, did schedule a hearing for next week to review state block grants and health care. That is not “regular order” as it’s usually thought of, but it is likely an attempt to assuage McCain’s process concerns.)

Murkowski and Collins are yet to take a definitive public position on Cassidy-Graham, but they have opposed every iteration of repeal so far. They have urged the Senate to pass a bipartisan health care bill and cast doubt that they could vote for a bill that rolls back Obamacare’s protections and overhauls Medicaid — which Cassidy-Graham does. On top of that, the CBPP estimated that Alaska would see its funding cut by $255 million in 2026 under the bill and Maine would lose $115 million.

So Collins or Murkowski would have to decide, after eight months of refusing to budge, that this is the Obamacare repeal plan they want to support.

Lastly, there is Paul, who has been the most prominent Republican critic of Cassidy-Graham over the past week. He has taken to Twitter repeatedly to blast the bill as an insufficient repeal of Obamacare and even sparred directly with Cassidy. He reiterated his opposition on Monday morning:

Graham/Cassidy keeps Obamacare and tells the states to run it. No thanks. — Senator Rand Paul (@RandPaul) September 18, 2017

No consevative should vote for a rebranded trillion dollar spending program just because it adds some block grants. — Senator Rand Paul (@RandPaul) September 18, 2017

Keeping 90% of Obamacare is not ok and it's not what we ran on. Conservatives should say no. — Senator Rand Paul (@RandPaul) September 18, 2017

Some people clearly doubt that Paul would be willing to be the 51st vote to stop Obamacare repeal, even if it’s a plan he doesn’t like. But the Kentucky senator (whose state would see a $3.1 billion cut in 2026, per CBPP) is digging in, not coming around.

If McConnell really is insistent on having 50 votes locked in before bringing Cassidy-Graham to the Senate floor, Paul is making that task more difficult.

The bottom line is that it could very well be that Senate Republicans are once again just a few votes shy of repealing and replacing Obamacare. They look ready to give it their all to get to 50 votes over the next two weeks. The threat to the health care law is real.

But whether Cassidy-Graham can secure a majority and succeed where every other repeal bill has failed isn’t clear at all. In fact, for now, the odds seem to be against it. But its proponents are betting that the pressure of the September 30 deadline will convince some of their colleagues to break.