Protesters in Washington rally against repealing and replacing Obamacare. (Nicholas Kamm/Agence France-Presse via Getty Images)

A YEAR into the Trump administration’s sabotage of Obamacare, the results are emerging. According to the Gallup-Sharecare Well-Being Index, the uninsured rate rose in 2017 by 1.3 percentage points — the largest single-year hike since 2008, when Gallup began collecting the numbers — to 12.2 percent. That may not seem like much. In fact, it works out to about 3.2 million more people lacking health-care insurance. That is a lot of real-world pain and suffering.

President Trump and Republicans have taken so many hostile steps that it’s impossible to attribute cause precisely to any single one. A year of negative rhetoric and rules changes may have deterred Americans from entering the system. Mr. Trump’s elimination of subsidies to insurers for participating in the Obamacare system rattled health-care markets. The president slashed Obamacare’s open enrollment period in half and cut its advertising and outreach budgets. Then, just as open enrollment was gearing up, Republicans in Congress added to their tax bill a repeal of Obamacare’s individual mandate, which requires Americans to carry health-care coverage if they can afford it. The loss of this important piece of Obamacare is only one recent change that could reverberate further over the coming year.

Some may look at the news with indifference, noting that when people are no longer forced to buy something, less of it will be bought. This has been a favorite argument of House Speaker Paul D. Ryan (R-Wis.). But few people actually want to find themselves without health insurance if they get sick. Moreover, when fewer people buy insurance, costs rise for everyone else.

The repeal-and-replace debate revealed that Americans by and large want the government to ensure that all people have health-care coverage. It is — and should be — unacceptable that more than a 10th of the country would face financial hardship in case of serious illness — or even to see doctors for more routine issues. Another 3 million people without coverage means another 3 million who will not be getting preventive checkups, who would struggle to obtain chemotherapy if suddenly diagnosed with cancer, who would show up to the emergency room with no insurance cards and need care to be paid for by everyone else if they got into an accident.

There are ways to contain this developing disaster, but it will require enough Republicans to decide to fix the nation’s health-care system rather than further sabotaging it. Sen. Susan Collins (R-Maine) voted for the GOP tax plan on condition that a bill she negotiated with Sen. Bill Nelson (D-Fla.) to shore up Obamacare marketplaces be considered. This was a poor trade-off, but it will look much worse if their bill ultimately fails to pass. Meanwhile, the Trump administration continues to propose rule changes that would further undermine the system; a particularly damaging policy would allow the sale of practically worthless plans companies could still call “health-care insurance.” These regulatory attacks should cease. Finally, states should fill in the gaps that Washington Republicans are opening. For example, they can impose individual-mandate policies within their own borders.

Obamacare was never perfect, but it was steadily bringing down the share of Americans without health insurance. Why would anyone want to reverse that achievement?