Republicans are still determined to repeal Obamacare, even though they have famously failed to unite behind an alternative. Now, it is dawning on some in the GOP that even if they succeed in repealing the Affordable Care Act, and even if they pass an alternative, they will still have to come up with a plan to get from here to there. Right now, they don't have one.

What is different about Republican calls for repeal today -- as opposed to calls for repeal from 2010 to the end of 2013 -- is that Obamacare is now in place. It exists. Exchanges are running -- many of them badly, but running. Subsidies are being paid. Insurance companies have changed the way they do business. Medicaid has been expanded. Special taxes are being collected.

Even though the system is new, millions of Americans have gone to a lot of trouble to adjust to it, and it would be disruptive to them to just stop cold. Halt subsidies? Undo Medicaid expansion? Just as last fall, when millions of Americans received coverage cancellation notices, millions more would face new burdens under the repeal of Obamacare.

"Rolling key provisions of the Affordable Care Act back would only create a new set of offended parties who would want to keep the insurance they have," health care analyst Robert Laszewski wrote recently. "Have you heard the one about, 'If you like your health insurance, you can keep it'?"

Republican plans are not designed to throw people onto the streets. But they will be different from Obamacare, and people will have to be covered in some way. And that will involve far-reaching changes in a system that people are still trying to understand.

"I have not seen very much in the way of discussion about a post-Obamacare transition," says one House Republican. "It's a good point, though -- repealing Obamacare doesn't bring us the health insurance market as it existed in 2009 [which would have been easier to reform] but leaves us with the system as changed by Obamacare."

The Republican notes that it's difficult to say precisely how the Affordable Care Act will work in the future because President Obama has unilaterally changed so many parts of it. For now, the Republican adds, the House GOP has focused mostly on general reform principles, although "at some point we will need to be able to explain to people how this will work in practice."

Obamacare appears to be performing poorly at its main goal, insuring the uninsured. A large percentage of those cited by the administration as new Obamacare private coverage signups were in fact already insured. A large percentage of those cited as new signups for expanded Medicaid were previously eligible. Still, all of them will have to be covered in some way under a new Republican-designed system.

Even though few in Congress have been thinking about transition, some of the more thoughtful conservative health care policy experts have. "A replacement for Obamacare might need a transition rule outlining some of the ways that people in exchange plans and the expanded Medicaid population could adjust to a new system," says Yuval Levin, a former Bush administration official who now edits the journal National Affairs. "But if the alternative is of the right sort it actually wouldn't be all that difficult."

Levin points to one GOP proposal, the Coburn-Burr-Hatch plan in the Senate. If it were to become law — there's zero chance of that anytime soon, but Republicans still hope — everyone now in an exchange plan could transition into a new private plan, without exclusions for pre-existing conditions. Obamacare's subsidies for purchasing insurance "would go away," Levin notes, "but a new tax credit for people up to 300 percent of poverty combined with the lower costs in the individual market would ease that transition significantly." The same tax credit would go to people currently eligible for Medicaid under Obamacare.

The point of a conservative alternative to Obamacare, Levin says, is for the system to "address our health-financing crisis by allowing providers to offer a genuinely broad array of options and allowing consumers to choose among them, rather than Obamacare's prescriptive approach that strictly defines the insurance product and then compels insurers to sell it and consumers to buy it."

Given that, Levin concludes: "It's much easier to transition from a prescriptive system to a more open system than vice versa."

Perhaps. But the bottom line is that if Republicans somehow had their way and were able to move the country to a post-Obamacare system, the process would involve imposing a sprawling set of changes on top of the sprawling changes that have already occurred during Obamacare. Even if it were all for the best, that's a lot of change. At some point, fatigue will set in.