In the debate over health care policy, Donald Trump and his team have already left a long trail of broken promises, but the White House nevertheless continues to make commitments it will never be able to keep.

Acting White House Chief of Staff Mick Mulvaney said Sunday that if the Trump administration succeeds in striking down the entirety of the Affordable Care Act in court, he can guarantee every person who has health coverage because of the Obama-era health law will not lose their coverage.

On “This Week,” ABC News Chief White House Correspondent Jonathan Karl asked Mulvaney whether he could provide such a guarantee for the millions of people who enrolled through HealthCare.gov, including those with pre-existing conditions and the people under the age of 26 enrolled under their parents’ plans.

“Yes and here’s why,” Mulvaney said Sunday. “Let’s talk about pre-existing conditions, because it gets a lot of the attention and rightly so. Every single plan that this White House has ever put forward since Donald Trump was elected, covered pre-existing conditions.”

The list of problems with this isn’t short. If the president’s scheme succeeds and the courts tear down the Affordable Care Act in its entirety, millions of families will lose their coverage. It’s an unambiguous fact. To hear the acting White House chief of staff tell it, none of those people should worry, however, because those Americans would maintain coverage in a post-ACA landscape.

No one should take this seriously – because there is no Plan B. Mulvaney boasted, for example, “Every single plan that this White House has ever put forward since Donald Trump was elected, covered pre-existing conditions.” That might be reassuring if (a) the White House had ever put forward a health care plan of its own; and (b) the White House hadn’t endorsed a variety of proposals from congressional Republicans that would’ve gutted protections for Americans with pre-existing conditions.

But stepping to look at all of this in the larger context, the root of the problem remains unchanged: GOP policymakers have spent a decade trying to craft an alternative to “Obamacare,” and they’ve failed repeatedly.

Trump and his Republican brethren seem to think this time will be different. They’re wrong – and it’s important to understand why.

On the surface, GOP officials are offering familiar rhetoric, repeated periodically since 2009, that the party’s blueprint is well on its way and will be available sometime soon. “There is a plan,” Kellyanne Conway told Fox News yesterday, adding that the Republican blueprint is “manifold.”

Reality, however, keeps getting in the way. As the Washington Post reported over the weekend, not only do Republicans not have a plan, “there are no plans to make such a plan.”

What about the Senate working group the president pointed to the other day? It now appears the group may not actually exist. Capitol Hill is looking to the White House to lead, the White House is looking to Capitol Hill to lead, and the result is a comedy of errors.

Stepping back, however, there’s a larger point that’s often overlooked. It’s easy to ridicule Republicans over their broken promises, bogus boasts, and imaginary plans, but the fact remains that there is no compelling GOP alternative to the Affordable Care Act because it’s an unobtainable goal.

Bloomberg News had a good report last week that noted in passing, “The problem for GOP lawmakers is the paucity of free-market policy ideas for health care that are politically popular.”

It’s an important detail. For 10 years, Republicans have tried to come up with a health care plan – which voters would actually like – that would bring coverage to millions and protect Americans with pre-existing conditions, without extensive regulation of private insurers, spending a lot of money, raising taxes, or increasing the deficit.

They’ve failed, not simply as a matter of governance, but also as a matter of logic. GOP officials are effectively trying to create a square circle. It can’t be done. It won’t be done.

Republicans are constrained in ways Democrats are not. When Dems began work on the Affordable Care Act, they set out to solve a problem. When GOP policymakers tried to address the same challenge, they set out to solve a problem in an ideologically satisfying way that honored conservative principles about taxes, regulation, and the size of government.

Those self-imposed limits necessarily made their task impossible. After a decade of Republican effort, nothing has happened because nothing can happen.

If GOP officials were sincere about coming up with a model that might meet muster, it would look an awful lot like the Affordable Care Act – which, despite a decade of hysteria, is already the centrist model based entirely on bipartisan principles.

Postscript: There are some reports this morning that Sen. Mitt Romney (R-Utah)) is in “preliminary discussions” about coming up with an ACA replacement plan for his party. Since Romney helped create the first-ever statewide coverage plan, that might seem like a sensible strategy.

The trouble, however, is that Romney’s model served as the basis for “Obamacare,” which Republicans have convinced themselves is unacceptable.