WHEN IT comes to understanding the Republican obsession to undo Obamacare, this number is about all you need to know: 24 million. That is how many people would lose coverage under the GOP’s supposedly choice-enhancing, access-increasing replacement plan. What possible justification can there be?

The estimate comes from the most trustworthy scorekeeper in the legislative business, the Congressional Budget Office (CBO). Despite a last-minute, irresponsible Republican campaign to discredit the CBO’s professionals, their view should carry far more weight than all the magical thinking the GOP has passed off as policy analysis in the health-care debate.

The CBO found that coverage would fall immediately, and then fall further after 2020, once the House GOP plan really kicked in. “The increase in the number of uninsured people relative to the number under current law would rise to 21 million in 2020 and then to 24 million in 2026,” the CBO reckoned. Here’s the alarming bottom line: “In 2026, an estimated 52 million people would be uninsured, compared with 28 million who would lack insurance that year under current law.” That’s a fifth of the non-elderly population left to fend for themselves, nearly double the current proportion.

Republicans have for years tried to ignore one essential trade-off in health-care policy: Cutting government spending on needy people’s care raises the number of uninsured, lowers the quality of coverage or both. Republicans say they can break this paradigm by unleashing the forces of local control, competition and consumer choice.

The CBO concluded that they cannot.

(Sarah Parnass,Bastien Inzaurralde/The Washington Post)

The Republican plan would cut Medicaid spending by $880 billion and subsidies for individual health insurance buyers by $232 billion over a decade, even as it loosened regulations that limit how much more insurers can charge older people than younger people and that require insurers to offer plans of a minimum quality. Premiums for older people would rise and for younger people would fall. Unsurprisingly, “a larger share of enrollees in the nongroup market would be younger people and a smaller share would be older people.”

The proposal would also cut subsidies aimed at the needy. Again unsurprisingly, “Fewer lower-income people would obtain coverage,” the CBO concluded.

Another iron rule the GOP cannot avoid is that insurers do not want all health-care customers, just healthy ones. They will use any leeway the government allows to offer skimpier coverage and serve only healthy people. The CBO found that the deregulatory push in the GOP bill “would lower the actuarial value of plans in the nongroup market on average” — in other words, erode the quality of the coverage people buy. Individuals’ cost-sharing payments, including deductibles, would rise, and especially from 2020, out-of-pocket costs for many lower-income enrollees would rise.

The net result: The GOP plan would reduce Medicaid enrollment by 14 million, cut enrollment in individual market health-care plans by 2 million and even reduce employer-provided insurance by 7 million people.

Republicans will note the CBO found that insurance markets would be stable under their plan. Yet their false alarms notwithstanding, insurance markets would be stable with some modest fixes to Obamacare, too. So we ask again: Why would anyone willingly harm the American people in this way?