It wouldn’t be 2017 if congressional Republicans weren’t trying to pass legislation to kill the Affordable Care Act.

And it wouldn’t be 2017 if there weren’t dual cases to be made that they may actually succeed — and that the likelihood of success looks extremely thin.

The advent of the Graham-Cassidy plan means the GOP has another chance to rebound from its stinging defeats on health care and fulfill its long-standing promise to overhaul the ACA. Doing so could take health insurance coverage or medical benefits away from millions of people, but with Republican leaders desperate for a strategic victory, and with less than two weeks to pass budget-related legislation with 51 rather than 60 Senate votes, they are working hard to persuade undecided lawmakers to vote yes.

Success is not guaranteed, of course. Notably, Congress's nonpartisan budget analyst has not said how much the bill would cost or how many people could lose health insurance. But proponents of Graham-Cassidy said they had momentum as the week began. Remember: The measure will die in the Senate if more than two Republicans vote no.

As the next two weeks unfold, here are the players to watch, starting with the senators expected to determine the bill’s fate.

Sen. Lisa Murkowski R-Alaska) was one of three Republicans to vote no on the last repeal attempt. (Joshua Roberts/Reuters)

• Sen. Susan Collins (R-Maine)

Collins is considered the most likely of any Republican senator to vote no on the legislation, which would transfer billions in federal health-care spending and policy authority to the states. Collins has expressed concerns about the measure, according to the Bangor Daily News, and Planned Parenthood's strong opposition to the bill could give her further pause.

During the last health-care vote, Collins didn't hesitate to be one of three Republicans to vote no. Without a significant rewrite (hint: losing a provision to defund Planned Parenthood), it's hard to see her switching positions on a measure that critics have called even more harmful than previous ones.

• Sen. Lisa Murkowski (R-Alaska)

Like Collins, Murkowski was one of the three Republicans to vote against the GOP's last attempt to undo the health-care law. And like Collins, she received warm thanks in her state after that vote. Even if the provision to defund Planned Parenthood were eliminated, it's not clear how the new bill, which by some accounts would negatively affect coverage for even more Alaskans, would move Murkowski to yes. But she tends to be somewhat more open to legislative dealmaking. So far, she has been silent on Graham-Cassidy.

• Sen. Rand Paul (R-Ky.)

Paul announced his opposition to the bill Friday, calling it "Obamacare Lite" and rebuffing an offer from co-sponsor Bill Cassidy (R-La.) to go over the details. On Monday, he said that nothing could change his mind.

Yet Paul’s past comments suggest that he could be open to cajoling, particularly if leaders are one vote short or if the bill undergoes changes.

"If they cannot get to 50 votes, if they get to [an] impasse, I've been telling the leadership for months now that I will vote for a repeal," Paul told ABC News in June. "It doesn't have to be 100 percent repeal. . . . That's what I want, but if you offer me 90 percent repeal, I'd probably vote for it. I might vote for 80 percent repeal."

• Sen. John McCain (R-Ariz.)

McCain stopped the GOP's last health-care push with a dramatic thumbs-down on the Senate floor. This time, he's vacillating in a way that suggests his vote is up for grabs.

When asked about Graham-Cassidy earlier this month, McCain said he would support it — then backtracked in a statement about assessing its effect on Arizona. McCain also said he wanted to consult with Arizona Gov. Doug Ducey (R), who has since endorsed the plan.

But not all signs point to McCain voting yes. On Sunday, he cautioned Republicans against the instinct to "ram through our proposal" without Democratic votes and complimented a separate, bipartisan effort to draft health-care legislation in the Senate Health, Education, Labor and Pensions Committee.

That effort is "doing fine," McCain told CBS. "Bring it to the floor. Have debate. Have amendments."

• Other possible swing votes

Collins, Murkowski, Paul and McCain are worth watching closely as the week proceeds. But other Republican senators could come out in opposition to Graham-Cassidy, throwing leaders’ math into doubt.

Sens. Rob Portman (Ohio) and Jerry Moran (Kan.), for instance, told reporters Monday that they were still reviewing the bill. Expect reporters to continue to grill them about it.

• GOP governors whose states expanded Medicaid

Ducey, Nevada's Brian Sandoval, Massachusetts's Charlie Baker and Ohio's John Kasich fall into an interesting political category: Republican governors whose states expanded Medicaid under the Affordable Care Act.

This means their states would have a lot to lose from Graham-Cassidy's Medicaid cuts. It doesn't mean all of the governors will oppose the bill, however. Although Baker and Kasich have criticized the plan, Ducey endorsed it Monday.

It's important to track the governors' positions because they could influence how Republican senators from their states vote. After all, it was Sandoval's opposition to one of the health-care bills this summer that drove Sen. Dean Heller (R-Nev.) to oppose it. (Heller supported the last version of an overhaul, known as the "skinny repeal," and is now a co-sponsor of Graham-Cassidy.)

• The Congressional Budget Office

This group of nonpartisan budget analysts holds enormous power in the current debate.

The CBO assesses bills’ impact on the federal budget before lawmakers vote on them, and it has often calculated how health-care measures would affect insurance premiums and the number of people with coverage.

These are politically potent figures that can determine how centrist lawmakers vote on health-care bills. But the CBO said Monday that it won't be able to release them "for at least several weeks" in the case of Graham-Cassidy. This means senators will decide their positions on the measure without the CBO's analysis of how it would affect premiums and coverage. It also means that the Senate will probably vote on the bill before the CBO releases its complete report.

• Sens. Cassidy, Heller, Lindsey O. Graham (R-S.C.) and Ron Johnson (R-Wis.)

These are the plan’s four original co-sponsors, and their political circumstances help illustrate why they joined on the bill.

Graham is up for reelection in 2020 and could throw his hat in the ring for president again. As a serious critic of President Trump, he will be looking for ways to reach out to voters who support the White House. Having his name first on the bill that repeals the Affordable Care Act would be a major selling point for a senatorial or presidential campaign.

Cassidy, a doctor, is a more junior member of the Senate who wants to shape health-care policy. Before partnering with Graham, he was working with Collins on a separate plan.

Heller is up for reelection in 2018. His role in legislation that cuts Medicaid could help him fend off a Republican primary challenger, but it could also make him more vulnerable in a general election in his purple state, especially if Sandoval opposes the bill.

Johnson is from a state that didn't expand Medicaid and whose governor, Scott Walker (R), supports the block-grant concept at the heart of the proposal. There's little political downside for him to sign on. Johnson is also a longtime critic of Senate Majority Leader Mitch McConnell (R-Ky.), who by some measures has the most to lose with the latest push.

• McConnell and House Speaker Paul D. Ryan (R-Wis.)

Republican congressional leaders face the prospect of ending the first year of GOP control in Washington without enacting the party's central policy priority of the past seven years. If Graham-Cassidy passes, the victory could relieve that burden and help shore up their relationships with the president. McConnell is under particular pressure because it was the Senate that sank the most recent attempt to pass a bill. If the latest effort fails, McConnell's culpability for inaction will only grow.

• Trump

Trump seems to have all but forgotten about health care, choosing instead to focus on tax reform and immigration. If he starts cajoling lawmakers, it could bring some undecideds toward yes — or, depending on his degree of tact, push them toward no.

Amber Phillips contributed to this report.