Call it an ObamaCare miracle. Despite hearing that the new president and the new Congress are threatening to destroy the Affordable Care Act, somewhere around 14 million Americans signed up for coverage in what may or may not be the law's final open enrollment.

Why did they do it? Perhaps because they just wanted to make sure they have insurance for the next year, or perhaps because they have no idea whether Republicans will keep their promise to "repeal and replace" the law. After all, it's complicated.

And there may be no more important phrase when it comes to the ACA, the repeal and replace effort, and health care reform in general: It's complicated.

The law gave insurance to 20 million Americans who didn't used to have it, and provided security for everyone, because we can no longer be denied coverage because of a pre-existing condition. Yet there are still millions without insurance (in no small part because of Republican governors who refused the law's expansion of Medicaid). And while growth in health spending and premiums has slowed, it hasn't reversed. There are still things people don't like about their coverage, like limited provider networks and high out-of-pocket costs. The situation in the individual market is better in some states than others. So much to consider!

Now compare that to what Donald Trump said about health care during the 2016 campaign: He'd repeal ObamaCare, and replace it with "something terrific." So much simpler!

But here's the thing: Democrats didn't make the ACA so complicated because they love complexity. They did it because they had no other choice. And now Republicans are confronting that same complexity in their effort to unwind what the Democrats did. There's just no way to do it simply or without unpleasant tradeoffs. It's that complexity that drives the dilemma Republicans find themselves in — and they can't find a way out.

Last week someone passed to reporters a tape of Republican members of Congress at a private meeting fretting about the consequences of their current effort at repeal and replace. While they expressed worries about the political fallout, as you'd expect ("That's going to be called TrumpCare," one said. "Republicans will own that lock, stock and barrel, and we'll be judged in the election less than two years away"), even more striking was their consternation over the substantive challenges of bringing such dramatic change to the health care system. How are we going to pay for it? What if the refundable tax credit we're thinking of doesn't offer people enough to afford coverage? What about the people who are left without the insurance they've recently gotten? They had lots of questions, but no answers.

They may even be starting to realize that there's a reason the ACA was so complex — and it wasn't Barack Obama's insatiable desire to force the heavy hand of government into your life.

In 2013, political scientist Steven Teles wrote an important article about the challenges of governing in which he argued that health care reform was a classic "kludge":

The term comes out of the world of computer programming, where a kludge is an inelegant patch put in place to solve an unexpected problem and designed to be backward-compatible with the rest of an existing system. When you add up enough kludges, you get a very complicated program that has no clear organizing principle, is exceedingly difficult to understand, and is subject to crashes. Any user of Microsoft Windows will immediately grasp the concept.

The bigger and more complicated the system, the more you'll find yourself applying a kludge if you want to change it — and there may be no more complicated system than health care. Our total spending on health care in 2015 was $3.2 trillion, or 17.8 percent of the entire American economy. Over 12 million Americans work in health care — a number that is increasing rapidly. Try to upend all that in one fell swoop, and you're in for a world of trouble.

When the Obama administration set out to enact health care reform, they looked at the experience of the failed Clinton reform effort in 1993 and concluded that its biggest political problem was that it changed the existing system in ways that people found too unsettling, particularly those in the employer-based system who were generally happy with their coverage. They also decided that the simplest system — some form of single-payer, or "Medicare for all" — threatened too many entrenched interests and could never pass Congress. So they tried to come up with a solution that would achieve their primary goals — getting as close to universal coverage as possible, guaranteeing coverage regardless of pre-existing conditions, and "bending the cost curve" — while causing as little disruption as they could.

The result was a gigantic kludge, an intricate clockwork mechanism with hundreds of interdependent parts. It maintained the employer-based insurance plan through which most working people get their insurance, added new protections, provided subsidies for those who had trouble affording insurance, expanded Medicaid for the poor and near-poor, and did dozens of other things nobody talks much about. Despite its successes, it didn't make things any simpler.

Democrats were willing to tackle this complexity because they sincerely wanted to fix the pathologies of the existing system. Republicans, on the other hand, never much cared. They'd do something on health care every now and again (like adding a prescription drug benefit to Medicare when George W. Bush was president), but it just wasn't an issue that animated them. Once it became Barack Obama's signature achievement, however, they started talking about health care all the time.

Yet they never had to confront the complexity of the issue — until now. They could just say "ObamaCare is a disaster! We'll repeal it!" and leave it at that.

But now they have to deal with all that complexity. What they're discovering is that every individual feature you want the system to have raises a series of questions, often ones that are difficult to answer. You want to cut costs? Then who loses out? Doctors, hospitals, insurers? You want to keep that pre-existing condition ban? Then where does the money to cover sick people come from? You want to allow cheap, limited plans? Then what happens when people find themselves without coverage? You want to reverse the growth of Medicaid? Then what happens to all the millions whose coverage you've taken away?

There are no simple answers to any of these questions. For a long time, Republicans could convince themselves there were — just get government out of the way, and everything will work out great. Now that they're responsible for the system, they're realizing how naïve they were to think it could be easy. But that's what happens when you keep telling people that the solutions to complex problems are simple.