Senate Majority Leader Mitch McConnell (R-Ky.) and other top Republicans speak at the Capitol in Washington. (J. Scott Applewhite/AP)

Things have gone from bad to worse for the Republican effort to dismantle the Affordable Care Act, also known as Obamacare. On Monday night, Sen. Mitch McConnell (R-Ky.) lacked the votes to pass a bill that would undo much of Obamacare and replace the law with a modified system. But the majority leader's back-up plan -- repealing Obamacare entirely right away, with the goal of working out a replacement later -- appears no more likely to succeed.

The dilemma for Republicans contemplating McConnell's new strategy -- repealing the law immediately and figuring out what to do next later -- is that Democrats may be able to stop them from carrying it through. While many Republicans would like to repeal Obamacare wholesale, they can't overcome Democrats' opposition without keeping in place some crucial components of Obamacare.

The GOP can't just repeal every word of Obamacare because, in order to avoid a filibuster by Democratic senators, Republicans are using a special set of rules known as reconciliation. Reconciliation makes legislation easier to pass, as it would allow the GOP to move the measure with just 50 votes and Vice President Pence's tie-breaker, rather than the 60 votes typically needed to break a filibuster.

The power has its limits, however. Reconciliation is only supposed to be used for measures that directly affect the federal budget. In this case, that means undoing some of Obamacare's taxes, fees, subsidies and safety net programs for the poor but leaving in place a series of health-insurance regulations and other features.

Republicans already did a dress rehearsal for this last year, when they used reconciliation to pass a bill through the Senate. That bill eventually died when it was vetoed by President Barack Obama, but now McConnell is advancing it again.

It's unlikely McConnell has the votes to the bill passed this time around. Short of a complete repeal, Republicans would risk creating something nobody in either party would support. With parts of Obamacare gone, some elements still in force and no new system to replace the law, patients and doctors would be left with a mishmash of incompatible regulations and requirements that would threaten to destabilize the health-insurance market and leave millions without coverage.

"It would throw the marketplace into chaos," said Stan Collender, a former congressional aide to Democratic lawmakers who worked on both the House's and Senate's budget committees.

Already, three Republicans -- Sens. Shelley Moore Capito (W.Va.), Susan Collins (Maine) and Lisa Murkowski (Alaska) -- have said they will not support McConnell's new strategy. Their combined opposition will probably prevent him from moving forward, although McConnell said Tuesday he plans to hold a procedural vote next week all the same.

Here's why some Republicans are skeptical.

What goes and what stays

Republicans would use reconciliation to eliminate taxes on the wealthy, on insurance providers and on medical companies.

They would also strike down a requirement that all Americans maintain health-care coverage or else pay the federal government a fee -- a controversial part of the law known as the "individual mandate." Republicans would eliminate another rule that requires major employers to offer an insurance program for their workers.

Republicans can also modify spending. The bill that McConnell aims to revive from last year would eliminate Obamacare's subsidies for people attempting to buy private health insurance.

Also, Obamacare increased funding for Medicaid, the federal insurance program that covers many poor households, pregnant women and residents of nursing homes. The GOP bill would undo that expansion.

Because these provisions apply to federal taxes and spending, Republicans can eliminate them through reconciliation. At the same time, other parts of the law would stay.

For instance, Republicans would likely be unable to remove protections for consumers with preexisting medical conditions who are trying to buy private insurance -- a crucial component of Obamacare. Likewise, insurers would remain unable to charge people depending on where they live or whether they smoke.

Insurers would still be required to offer certain benefits as part of their plans, as they are under Obamacare, and limits on how much more they can charge older customers would remain in effect.

Preexisting conditions

In short, the legislation would preserve some rules from Obamacare, while eliminating much of the rest of the law. The odd combination could result in serious problems, industry analysts warn.

Before Obamacare, for example, insurance companies were free to charge patients more if they had preexisting conditions, or to deny those customers coverage entirely. That practice existed to ensure that private insurers could break even. Without some way of discouraging the sickest patients from seeking coverage, the cost of treatment would increase uncontrollably.

Obamacare ended that practice, prohibiting insurers from discriminating against patients based on their medical histories. Instead, Obamacare required all Americans to maintain coverage and offered subsidies to encourage them to do so. The goal was to guarantee that insurers would have enough healthier customers paying monthly premiums to cover costs for sicker patients.

The bill McConnell will hold a vote on next week would get rid of that financial assistance and the requirement. Yet it would not allow insurers to examine their customers' medical histories again. Most experts believe that language undoing Obamacare's protections for patients with preexisting conditions would not qualify under reconciliation.

As a result, the only legislation Republicans might be able to pass would restore the system that existed before Obamacare, but without a crucial feature that allowed that system to function. The resulting mismatch -- between rules Democrats established under Obamacare and those that existed before -- could prove an embarrassing failure for GOP lawmakers.

"The market could literally disappear entirely," said Edwin Park, a vice president for health policy at the liberal Center on Budget and Policy Priorities.

Millions uninsured

That, in essence, is what many analysts are projecting for a GOP bill that partially repeals Obamacare without a replacement.

Insurers would hike premiums to cover the steeper cost of providing health care to a sicker group of patients. Only patients with serious medical problems would be willing to pay those costs, so healthier patients would cancel their policies. In turn, insurers would be forced to increase premiums even more, and so on.

In an analysis in January, the nonpartisan Congressional Budget Office (CBO) forecast that simply repealing Obamacare without a replacement would eventually result in 32 million more Americans going without coverage. Almost immediately, premiums would skyrocket, increasing by 20 percent to 25 percent in the first year on average.

Companies would refuse to sell insurance across swathes of the country because so few patients would be willing to pay the exorbitant premiums insurers would have to charge to turn in a profit while covering a large group of relatively unhealthy patients. In those areas, Americans would have no options for buying private insurance if they did not receive it through the government or an employer. About 10 percent of Americans would live in these areas in the first year, CBO estimated.

If Republicans failed to come up with an alternative system, that figure would eventually increase to 75 percent of the population, while premiums in the individual market would double.