Washington (CNN) Disagreement among Democrats over how to achieve universal health care exploded again into view Thursday night as hopefuls took the stage for the second 2020 Democratic presidential nomination debate.

Universal care may be the single biggest issue dividing the Democratic primary debate stages. Should people be given the option of a government-run health care plan or should it be forced upon them?

And among the most difficult facets for Democrats to answer is: What can Democrats actually do about it?

Of the 20 candidates on the two debate stages Wednesday and Thursday, just four raised their hands when asked who backed the elimination of private health insurance.

Bernie Sanders has been talking about this for some time. His Medicare for All plan, a mandated single-payer system, is the dream of some progressives. While every Democrat has paid lip service to the idea of a government option, Sanders would make the government option the only one.

The other lawmakers backing Sanders' idea and raising their hands were Sens. Elizabeth Warren of Massachusetts and Kamala Harris of California, along with New York City Mayor Bill de Blasio. Notably, two cosponsors of Sanders' bill -- Sens. Kirsten Gillibrand and Cory Booker -- did not raise their hands. Neither did House members Eric Swalwell or Tulsi Gabbard, who have cosponsored a similar version.

Other Democrats back the creation of a public option that would be an alternative to private health insurance but not replace it -- at least not right away.

Health care in America: By the numbers

JUST WATCHED Democrats took it to the mat on night two of the debate Replay More Videos ... MUST WATCH Democrats took it to the mat on night two of the debate 02:49

While Sanders' Medicare for All plan includes a four-year transition period, it's still hard to imagine the complete transformation of the US health system in that time. We're talking about new health insurance for more than 150 million people. The implementation of the Affordable Care Act was much much smaller. And voluntary. And a complete and total disaster at the beginning.

Thirty-six percent of Americans have some form of government health insurance already -- 21% have Medicaid, 14% have Medicare and 1% have another form of public insurance, according to Kaiser Family Foundation's analysis of 2017 Census data

But a lot more have private insurance. Nearly half -- 49% -- of Americans get private health insurance through their employer and another 7% have non-group insurance. That leaves 9% uninsured. And many who have private insurance complain it is way too expensive.

"I find it hard to believe that every other major country on Earth, including my neighbor 50 miles north of me, Canada, somehow has figured out a way to provide health care to every man, woman, and child, and in most cases, they're spending 50% per capita what we are spending," Sanders said.

He tweeted a list of countries that have universal health care coverage, while nearly 10% of the US population goes uncovered.

Universal health care is not a radical idea. It is a reality in:



Australia

Austria

Belgium

Canada

Chile

Czech Rep.

Denmark

Finland

France

Germany

Greece

Hungary

Iceland

Israel

Italy

Japan

Netherlands

New Zealand

Norway

Poland

Portugal

S. Korea

Spain

Sweden

U.K.#DemDebate2 — Bernie Sanders (@BernieSanders) June 28, 2019

But there's a huge difference between universal coverage -- where everyone has access to health care -- and a government-run system. Not nearly all of the countries on Sanders' list outlaw private insurance. In fact, even in Canada, most vision and dental coverage is private.

That was a criticism of Colorado Sen. Michael Bennet, who complained that Sanders would undo all types of health insurance except for plastic surgery.

South Bend, Indiana, Mayor Pete Buttigieg, who wants to start with a public option as a "glide path" to a single-payer system, said it's not clear to him how else to get to Medicare for All.

"Everybody who says Medicare for All, every person in politics who allows that phrase to escape their lips, has a responsibility to explain how you're actually supposed to get from here to there," he said.

Sanders' lack of details on how to implement Medicare for All

And this continues to be the big difficulty for Sanders. He was actually asked at the debate how he exactly he would enact Medicare for All.

"I will tell you how we'll do it," Sanders said. "We'll do it the way real change has always taken place, whether it was the labor movement, the civil rights movement, or the women's movement. We will have Medicare for All when tens of millions of people are prepared to stand up and tell the insurance companies and the drug companies that their day is gone, that health care is a human right, not something to make huge profits off of."

That's a really good way to explain how people who support Medicare for All can lobby for it. But it does very little to answer the question of how he'd actually do it.

Senate Majority Leader Mitch McConnell, the self-styled grim reaper of liberal policies , is more than likely to be Senate majority leader in 2021. And he's not going to let Medicare for All become law.

Sanders has always been more interested in a revolution than a single piece of legislation, and starting a movement behind change is by its nature a very long process.

But Sanders did not own up Thursday to the political realities his proposal faces.

Beyond McConnell and unified Republican opposition to a single-payer plan, there was the proof on the debate stage that every Democrat wouldn't be likely to fall in line behind it.

Backlash to the Affordable Care Act cost Democrats control of the House in 2010 and they only just regained it this year.

While Sanders is right that public opinion polls show support for the idea of Medicare for All and a single payer plan has grown -- 56% -- in support, according to an April Kaiser Family Foundation poll. There's much more support -- 75% -- for the half-measure of government buy-in. There's also a clear partisan divide hidden in those numbers. And there is much less support when people are asked if private insurance should be outlawed.

Has the national mood on health care shifted?

The great difficulty for President Barack Obama after enacting the Affordable Care Act was a failure to live up to his pledge that, "if you like your health care plan, you could keep it."

Sanders' plan would start from a place of half the country cannot keep their health care plan.

It's possible the national mood has shifted in the past 10 years, but that would be a huge change indeed for such a proposal to be enacted.

"People don't like their private insurance companies," Sanders said at the debate. "They like their doctors and hospitals. Under our plan people go to any doctor they want, any hospital they want."

But fewer doctors accept Medicare than private health insurance. Doctors facing lower reimbursement rates under Medicare for All might go up in arms about Sanders' plan.

All of this means that Sanders needs a much more specific, realistic answer when he's asked the question of how he'd accomplish Medicare for All.