Mitch McConnell has warned that if Republican attempts to replace Obamacare fail, then his party would be compelled to work with Democrats to stabilize insurance markets. Whether that statement was intended as a threat or just a reflection of a political reality could be determined soon with an expected Senate vote on the newest iteration of the GOP plan.

At least one Republican senator is embracing the majority leader’s ultimatum. Maine’s Susan Collins, the most outspoken critic of the legislation, has said she would not even support a procedural motion to open the bill for debate and a vote. Instead, she said she stands ready to work with colleagues on both sides of the aisle “to fix the flaws in the ACA.”

While Collins by no means reflects the sentiments of the Republican conference in the upper chamber, several members have expressed concerns about the new version of the bill, putting its passage in jeopardy. The legislation repeals insurance mandates under the current law, but keeps in place some of the Affordable Care Act’s tax requirements in order to pay for spending to combat opioid addiction. It also includes a provision intended to woo conservatives that would allow insurance companies to sell cheaper plans with fewer benefits.

Majority Leader McConnell originally planned a vote this week to move forward with the measure, but postponed it because Sen. John McCain would be absent as he recovers from emergency surgery to remove a blood clot. The delay underscored the legislation's fragility, as the GOP can't afford to lose any more votes.

Meanwhile, Democrats have embraced Collins’ overture, and plan on using the coming week to apply more pressure on the GOP. As Republicans struggle to find the needed 50 votes, the minority party has been positioning itself as a willing partner in fixing the existing system -- so long as Republicans drop their years-long pledge to repeal the law. Democrats’ unified opposition to the GOP plan has added energy to their base, as health care is often an emotional and contentious campaign issue.

But the process has also highlighted their limited resources as the out party in Washington. These lawmakers are challenged with balancing the ideals of their party -- a “Medicare for all” system has become a recent rallying cry among Democrats around the country -- with the political reality at hand.

Indeed, Democrats aren’t underestimating the ability of the GOP leader to eventually get his members on board. And they acknowledge that even if the repeal plan fails, the parameters of any subsequent negotiations would be narrow.

"If you’re sitting down with Republicans, I think we’re talking about a limited package to address stability and flexibility on the exchanges," Connecticut Sen. Chris Murphy told RCP. Asked about his confidence level that matters would reach such a point, he described it as “low-. Not nonexistent, but low."

But first things first. "I am squarely focused on defeating the repeal bill," said Sen. Tammy Baldwin, a Wisconsin progressive. "Nothing else matters until we do that."

Hawaii Sen. Brian Schatz acknowledged that Democratic wish-list items would likely be off the table in a negotiation: "But let’s take this one step at a time. The first step is to kill this awful bill, and then we can start talking about bipartisan negotiations."

"If we get to the table, it’s the art of the possible," said New Jersey Sen. Bob Menendez. "I’d love to see a single-payer system, but I don’t think that’s negotiable. But I do think it is ‘How do we stabilize the insurance market? How do we do better on end-of-life care? How do we do better on chronic disease?’ ... There’s a lot we could do together."

Sen. Sherrod Brown of Ohio, who is up for re-election next year, said Democrats are interested in fixes that stabilize the insurance pool, bring more young people into the program, and go after abuses by drug companies. Brown says he’s ready to negotiate with Republicans, “but I’ve taken [McConnell’s] word before and not have him honor it.”

For their part, Republicans are still a long way off from thinking about negotiations.

"If we fail here, we come right back, in my opinion, to the health-care conversation and we do that in a bipartisan fashion with Democrats holding the ace," South Carolina Republican Sen. Tim Scott told Fox Business Channel. "That is not where we want to be.”

In the meantime, they have been aiming to gin up support for their plan by railing against Democrats’ calls for a single-payer system, a proposal that failed to attract enough support when the party controlled Congress and the White House during the drafting of the Affordable Care Act. Now, however, the system in which government finances all health care coverage is a rallying cry among the base. Bernie Sanders championed it during his presidential run, and has been traveling the country holding health care rallies in states Trump won. Elizabeth Warren has called for Democrats to run on single payer. And others in the party considered to be presidential contenders have begun to warm to the idea.

Republicans see this as working to their advantage, and aim to hang support for the system around the necks of Democrats. "They intend on catering to the demands of Elizabeth Warren instead of their constituents," said Matt Gorman of the National Republican Campaign Committee.

In a speech on the Senate floor last week, McConnell warned his GOP colleagues of the options that would be left to them if they failed to pass their bill. "Another idea, from many other Democrats, is to quadruple-down on Obamacare with a government-run single-payer system," he said. "Nearly every health-care decision could be decided by a federal bureaucrat. Taxes could go up astronomically. The total cost could add up to $32 trillion, according to an estimate of a leading proposal."

Other Democrats have suggested revisiting the idea of a public option, an idea explored by Democrats during the conception of Obamacare but that narrowly failed to get requisite support.

Pennsylvania Sen. Bob Casey, who is up for re-election next year, picked up on this concept: “If this bill goes down, and we move to the next chapter where we are actually having bipartisan conversations, one thing we can say is ‘OK, if you’re in a rural area, and there’s only one insurer and rates and premiums are up because there’s no competition, how about a Medicare-like public option in that community to create immediate competition in that particular market?’ We debated this a couple of years ago, but it hasn’t really been debated in a long time.”

The idea has long been championed by former Vermont governor and presidential candidate Howard Dean. But Dean acknowledges that Democrats are far from pushing that kind of proposal so long as Republicans are in control in Washington. The vision is likely to become more prominent on the campaign trail in the next presidential race, if not the midterms.

Dean says Democrats can sell a public option plan that would allow those not yet eligible for Medicare to buy into a similar program. “We're going to get a lot farther in the politics of this country if we let people choose to be in single payer and not tell them they have to be in one,” he said. “It has to be a gradual transition … to open the door to let the American people decide for themselves instead of having government tell them what to do.”

While Hillary Clinton did not embrace the single-payer program during the primary against Sanders, she did support a “Medicaid for more” type of plan to allow those of a certain age to buy into government-subsidized coverage.

In their party platform, Democrats described health care as a right. The platform also described Obamacare as “a critically important step toward the goal of universal health care.”

House Minority Leader Nancy Pelosi said that while she has long supported the idea of a single-payer program, she does not think it should be the party's calling card in the midterms. "If you want that, do it in your states, as states are laboratories and could work," she said at a press conference this year. "The comfort level with the broader base of the American people isn't there yet."

More than 100 House Democrats have signed on to a single-payer bill by Rep. John Conyers. Sanders is planning to unveil his own health care bill in the Senate at a later date. But Democrats are also having difficulty enacting legislation in the states. Vermont, for example, pulled the plug on a single-payer proposal for economic reasons. A similar bill in the California state legislature has stalled.

Proponents point to data points showing an eventual public appetite for such reforms. A recent Pew study, for example, shows 60 percent believe the federal government is responsible for ensuring health care coverage for all Americans, while 39 percent disagree. But just 33 percent favor a single-payer approach, though the study notes that has increased five percentage points since the beginning of the year.

For now, though, congressional Democrats say they are focused on the immediate task at hand, and are mindful of the ways in which Republicans are messaging on the issue.

“I think it’s a wonderful theoretical exercise that Republicans would like to have Democrats spend all their time talking about,” Murphy said when asked about single payer. “What I’m focused on this week and next week is about the Republican health care proposal.”