Bernie Sanders waves after delivering a speech at Georgetown University on Nov. 19, 2015. (Carlos Barria/Reuters)

Maybe the revolution got started just a little too late.

For decades, Bernie Sanders has been advocating for national health insurance. During his improbable ascent to national prominence over the past year, his desire to provide every American with publicly funded insurance has defined his Democratic presidential primary contest with Hillary Clinton. Although he campaigned on other issues as well — Wall Street, free college and the war in Iraq — his most ambitious goal has been replacing today's patchwork health-insurance system with one run by the government.

And although health care may have helped take Sanders further than anyone expected, he continues to lag badly with delegates, and the chances of him winning the nomination are increasingly slim.

One interesting question is why health care didn't help him more. Americans are interested in alternatives to the current system. Many would be willing to replace it with something similar to what Sanders has proposed, also known as a single-payer program. Seventy-three percent of Democrats in a Gallup poll said they would favor replacing President Obama's Affordable Care Act reforms with "a federally funded health-care program providing insurance for all Americans." Even 41 percent of Republicans said they would prefer a single-payer system to the existing one.

There are clear reasons for Americans' dissatisfaction with the system Obama established. Twenty-nine million people remain uninsured, more than 1 in 10 people, many of them in states that have not expanded Medicaid under the law. Almost half of the uninsured say they still can't afford coverage.

"You can’t really imagine a less well functioning system than the U.S. one," said Jacob Hacker, a political scientist at Yale University. "From a progressive political standpoint, you've got a major policy disaster here."

But if American health care is a policy disaster, the progressive candidate who says he has a fix doesn't seem likely to win. Here are four reasons that health care may not have been a winning issue for Sanders this year.

1. Far fewer people are uninsured.

Today's system of health insurance -- which combines Obama's Affordable Care Act with employer insurance and government insurance for the poor, elderly and veterans -- does not have the elegance of national health insurance, and it has plenty of flaws. But far more people are insured under the law commonly known as Obamacare than have been throughout Sanders's political career.

As Larry Levitt, a senior vice president at the Kaiser Family Foundation, pointed out, it is quite possible that there has never been a time in American history where fewer Americans lacked decent health-care coverage.

"We're not at universal coverage, but we’re a whole lot closer than we were a few years ago," Levitt said in an interview.

Overall, non-elderly African Americans and Latinos are uninsured at significantly higher rates -- 11.2 percent and 20.8 percent, respectively -- than white Americans, of whom only 7.2 percent lacked coverage in 2015.

Yet blacks and Hispanics are much more likely than before to have insurance. The rate of uninsured Hispanics has declined by a third since 2010, according to the Centers for Disease Control and Prevention, and the rate among African Americans by nearly half.

2. More people are getting help to buy insurance. 

Obamacare reduced uninsured rates largely by providing financial help to families. As a result, there is not as much left to do for a single-payer system when it comes to helping families economically, a major priority for Sanders and his supporters.

Under the law, many states expanded Medicaid, the health insurance program for the poor created by President Lyndon B. Johnson. Families that didn't qualify for Medicaid could receive subsidies from the federal government to buy insurance privately through the exchanges created by the law.

Sanders's system would make public insurance available to all Americans, free of charge. Yet because he would replace the existing benefits under Medicaid and Obamacare, his proposal would have the surprising effect of directing new spending primarily to wealthier households, rather than the poorer ones that have been the focus of his campaign.

An analysis published last week by the nonpartisan Tax Policy Center illustrated this point, showing that new governmental transfers to the wealthiest one in five households would be almost double the new transfers to the poorest one in five under Sanders's plan, accounting for the lost benefits from Obamacare and Medicaid.

The richest would almost certainly pay more in taxes than they would gain from Sanders's proposed spending on health care, but it is unclear how much money would have to be raised in taxes to fund the plan, and who would pay.

Independent analysts have said that Sanders hasn't identified enough new revenue sources for the government to pay for his system. The Tax Policy Center projects that the cost would total $32 trillion over 10 years, while Sanders has proposed only $15 trillion in new taxes.

Meanwhile, although some poor families would stand to gain from his programs, the benefits would be distributed unevenly, with substantial improvements for patients in need of long-term medical care, for example.

The working poor could even be worse off if they receive Medicaid, because their health-care benefits would not be substantially expanded under Sanders's plan and they might have to pay more in taxes, noted Kenneth Thorpe, a former health official in the Clinton administration.

"There are a lot of households who will pay more in taxes than they’re going to get in any type of benefits," Thorpe said. He calculates that accounting for the taxes needed to fund Sanders's system, 85 percent of working families on Medicaid would be made worse off financially, along with 71 percent of working families with private insurance.

Warren Gunnels, Sanders's policy director, has disputed the estimates from Thorpe and the Tax Policy Center, saying they underestimate the savings under a single-payer system. Gunnels argues that Sanders would not have to raise taxes on the middle class and the poor beyond the new ones he has proposed.

"The fact of the matter is that the U.S. spends far more per capita on health care with worse health outcomes than any major country on earth," Gunnels said in a statement last week. "If every other major country can spend less on health care and insure all of their people, so can the U.S."

3. Americans aren't spending much more on health care.

Another reason that Sanders's timing might have been less than ideal is that health-care expenditures have been increasing more slowly. The issue of costs has become less urgent as a result of the trend, which is a relief for American families.

Insurance is still unaffordable for many. Even those who have it are often stuck with exorbitant deductibles and coinsurance if they go to the hospital. Kaiser's Levitt and his colleagues found that the typical subscriber in employer-sponsored plans paid $353 a year toward deductibles, nearly three times more than a decade ago.

Overall, though, Americans are not spending much more on health care than they were a few years ago, a major shift from the past.

Between 1960 and 1990, according to federal data, national spending on health care increased by an average of more than 10 percent per year. Spending continued to increase rapidly until about 2007, when the financial crisis forced many households to save money by postponing visits to the doctor.

Since then, expenditures have continued to increase, but at more subdued rates, according to monthly data from the Altarum Institute. The shift is largely a result of what Levitt called the "lingering effects" of the crisis.

"I don’t think we fully understand how far-reaching the recession was in holding down consumer spending generally and health spending specifically," he said.

Levitt also said that provisions in Obamacare designed to constrain costs, along with a broader shift toward electronic medical records in clinics and hospitals, may have made the health-care sector more efficient.

4. Voters aren't as concerned about health care.

It seems that Obamacare and the economy may have addressed many Americans' concerns about the health-care system. Gallup's polling suggests that voters aren't as worked up about the issue as they were even just a few years ago.

In recent presidential elections, the share of Americans telling pollsters that health care is the country's most important issue was often above 10 percent. That figure had declined to 4 percent in Gallup's latest poll.

In other words, the kind of overwhelming popular anxiety about health care that could create the political momentum for radical change just isn't there anymore.

"I’ve always figured that if single payer were going to happen in this country, there would have to be some crisis that precipitated a sense that the health care system was collapsing and needed to be reworked in a major way," Levitt said. "We’re certainly not at that stage now, and in fact, we’re in a period where many of the goals of a single-payer system are much closer to happening than they were before."

Sanders has spent years campaigning for single-payer health care, but he and his supporters may have to go on waiting.