This post was originally published in June and has been updated several times with Republicans' various failed attempts to repeal Obamacare.

After six tumultuous months, Republicans have finally waved the white flag on repealing and replacing Obamacare.

The House of Representatives barely passed a version in May undoing some parts of Obamacare, but the Senate hasn't even come close. Their last-ditch attempt merely to repeal Obamacare's individual mandate crashed and burned late Thursday night.

But nearly every Republican in Congress can agree with what House Speaker Paul D. Ryan (R-Wis.) said recently: Repealing and replacing Obamacare is a big deal for Republicans' electoral hopes.

“I think it's probably the most, it's the biggest signature issue we have,” Ryan told “Fox & Friends.” “And it's the biggest promise we've ever made in the modern era. We said if we get elected, we will repeal and replace Obamacare.”

So why can't they do it?

I've been following this closely and speaking with nonpartisan health-care policy experts and political observers throughout this messy process. I've come up with a few, not mutually exclusive theories as to why it's really, really hard for Republicans to actually pass a health-care bill even though they all want to.

1) They underestimated how hard stopping a social program in its tracks would be

Saying: “I'm going to repeal and replace Obamacare” takes about 3.5 seconds. (I timed it.)

But apparently it takes more than seven years to actually do it. When Republicans got full control of Washington in January after seven years of promising to repeal Obamacare, they didn't really have a plan.

Maybe they thought it was going to be easy once they controlled all levers of power. More likely, they weren't sure how to roll back a major social program that 20 million people now rely on to manage the most personal of all things, their health.

"They didn't expect to win, and they hadn't really explored what to do if they did," said Alice Rivlin, of the Brookings Institution.

Republicans needed a well-thought-out plan. You can't repeal something without immediately having something to replace it with, Gary Claxton, an analyst at the nonprofit Kaiser Family Foundation, told me in January when this whole process was getting started.

“The longer the period between repeal and replace is, the more the market unravels,” Claxton said. “And you've blown up the bridge behind you, and you're heading into battle. You can't go backward. You've gotta figure it out, or else things get really bad.”

Instead, largely behind closed doors, they slapped something together.

2) They underestimated how ideologically varied their party has become

Republican leaders have been grappling for years with a growing bloc of principled conservatives who are politically rewarded in their conservative districts for not compromising.

But it feels as if they were caught off guard by an equally influential, somewhat larger and just as intransigent faction of moderates.

Those moderates campaigned on repealing Obamacare, but when it came time to pull the lever that would take away health care for hundreds of thousands of their constituents, they just couldn't politically do it.

As for Thursday's late-night vote in the Senate, conservatives had made peace with just getting rid of Obamacare's individual mandate, but two moderates, Sens. Susan Collins (Maine) and Lisa Murkowski (Alaska), along with Sen. John McCain (Ariz.), sunk that proposal early Friday morning.)

(Kim Soffen/The Washington Post)

Now, this group seems to be suggesting it would be better to work within the existing structures of Obamacare than take its benefits away.

In a no-holds-barred speech on the Senate floor earlier this week, McCain ripped apart Republicans' repeal strategy: "We’ve tried to do this by coming up with a proposal behind closed doors in consultation with the administration, then springing it on skeptical members, trying to convince them it’s better than nothing, asking us to swallow our doubts and force it past a unified opposition. I don’t think that is going to work in the end. And it probably shouldn’t."

3) They're trying to do it without Democrats

Yes, Democrats passed Obamacare in 2010 without any Republican votes. (Though Democrats say they tried: “We spent months — at the detriment of the process — trying to get Republicans on board, only to give up,” said Jim Manley, an aide to Senate Democratic leadership at the time.)

Forging ahead on major legislation solo is a problem for the party doing the forging for three reasons:

  • When you try to pass something with just one party, you have to rely on fewer votes. In 2010, Senate Democrats barely passed Obamacare, and they had 60 members. This time, Republicans have 52. “There is just not a majority of Republicans around any one approach to this problem,” Rivlin said.
  • To avoid a Democratic filibuster, Republicans have to abide by a budgetary rule that limits how much of the health-insurance market they can actually change, which limits their ability to make substantial changes to Obamacare.
  • Whatever happens with people's health care after this, Republicans will own it. That's why the prospect of millions fewer insured over the next decade was a hard vote for a sizable chunk of the party to take. Drew Altman, president of the Kaiser Family Foundation, said of the Senate's first version of the bill: "I don't think we've seen a major major piece of legislation that has many many, many more losers than winners, and that's what they've wound up with."

Here's an estimate of how the Senate's proposal to repeal and replace Obamacare would have messed with the insurance rolls:

(Kim Soffen / The Washington Post)

4) They don't have a president they can rely on

President Trump has been largely invisible in this process, and when he has been visible, he's arguably mucked it up.

When the House was trying to drag its bill across the finish line, Trump seemed uninterested. Until it failed, at which point he attacked various Republicans in the process. Then it passed, and Trump held a triumphant Rose Garden ceremony with House Republicans.

The celebration. (Carlos Barria/Reuters)

Republicans in the Senate say Trump gave them little guidance about what he wants or what he'll sign -- other than to say that the bill he cheered on in the Rose Garden was “mean” and that he wanted something “with more heart.”

And after it failed, Trump waved his own version of a white flag: Just let Obamacare implode. (Never mind the risk that Republicans will be blamed for the health-insurance markets' demise.)

The president of the United States has enormous leverage to be a closer. But most of the time, Trump appears to be ignoring the process or directly undercutting it. Which isn't helping Republicans complete what now seems to be an impossible task: to repeal and replace Obamacare.