It is a common refrain from Bernie Sanders on the campaign trail: The United States is the only developed country that does not provide health coverage to all residents.

“Canada can provide universal health care to all their people at half the cost,” he said at a recent Democratic debate. “The U.K. can do it. France can do it. Germany can do it. All of Europe can do it.”

Mr. Sanders is right: All these countries provide universal coverage. But what he doesn’t talk about is the excruciating battle they went through to get there.

It took Canada more than a decade to move from a patchwork of insurance plans to a single-payer system. At one point, doctors were so incensed that they went on strike for 23 days. Doctors from the United States and Britain flew in to help keep the health system going.