"This is a pivotal moment in American history," Sanders writes. "Do we, as a nation, join the rest of the industrialized world and guarantee comprehensive health care to every person as a human right? Or do we maintain a system that is enormously expensive, wasteful and bureaucratic, and is designed to maximize profits for big insurance companies, the pharmaceutical industry, Wall Street and medical equipment suppliers?"

CNN provides an assessment of some of the bill's details expected to be unveiled Wednesday: Americans would receive a "Universal Medicare card" for a comprehensive list of health care services, including hospital stays, doctor visits, substance abuse treatment, dental, vision and reproductive care — including abortion. However, consumers may have to pay up to $250 out-of-pocket for prescription drugs, with incentives to use generic medications, and the federal government would be allowed to negotiate with pharmaceutical companies.

"While the new legislation has not yet been scored, the program Sanders pitched on the campaign trail came with an estimated annual price tag of nearly $1.4 trillion, to be paid for in part by a proposed new 2.2 percent income tax on all Americans, a 6.2 percent levy on employers and a further round of tax hikes on the wealthy," CNN writes.

NBC News' First Read cites a June 2017 Kaiser Family Foundation poll, which found 53 percent of Americans supporting single-payer, and 57 percent support the concept when it's called "Medicare for All."

"But that's not the entire story: When respondents were presented with an argument that single-payer/"Medicare for All" would raise taxes, opposition grew from 40 percent to 60 percent," First Read writes. "And when presented with an argument that the plan would give the government too much control, disapproval went up to 62 percent."

Related: Americans have no idea where their tax dollars go

The bill isn't necessarily intended for passage any time soon while Republicans control Congress, Elise Viebeck and David Weigel write in WaPo's Today's Prognosis.

"The support it is generating is significant, however, in showing how the Democratic Party has lurched leftward since Donald Trump's election, and telling of where Democrats will head as the party prepares for 2020," the two write.

Among the co-sponsors who are also possible presidential contenders are Democratic Sens. Elizabeth Warren (Mass.), Kamala Harris (Calif.), Corey Booker (N.J.) and Kirsten Gillibrand (N.Y.), and on Wednesday came Al Franken (Minn.).

"But the issue holds danger for Democrats now that they are considering the legislative realities and not just pie-in-the-sky visions," writes the New York Times's Margot Sanger-Katz: "Leaders of liberal states saw support for the idea erode as they confronted those political realities. In Vermont, the framework of a single-payer system passed the state legislature in 2011, only to be abandoned after experts estimated the system would require the state to double its tax revenue."

Sanger-Katz quotes Obama Centers for Medicare and Medicaid head Andy Slavitt, who "worries that the quick shift among his peers on single-payer could backfire. 'That could be the Democrats' version of the thing that they promised to do for seven years and couldn't do.' "

Neither House Minority Leader Nancy Pelosi (D-Calif.) nor Senate Minority Leader Chuck Schumer (D-N.Y.) have not signed on to Sanders' plan. Pelosi tells the Washington Post that support for a Medicare-for-All proposal won't become a "litmus test" for the party.

"I think to support the idea that it captures is that we want to have as many people as possible, everybody, covered and I think that's something that we all embrace," Pelosi says. She wants Democrats to consider a variety of options, but said she doesn't think much will succeed until Republicans stop attacking the Affordable Care Act.

Many other Democrats aren't committing support to Sanders' bill, writes Politico's Elana Schor. Sen. Claire McCaskill (D-Mo.) says that lawmakers have more work to do to keep health care costs in check "before we would think about expanding that [Medicare] system for everyone."

John Merline writes in Investors Business Daily that Sanders and the co-sponsors never mention that other countries with some sort of government-funded health care system require "a far bigger share of health care dollars out of pocket than the U.S. does today, or that most of them have some form of private health insurance in the mix."

Australians pay nearly 20 percent out-of-pocket costs, Swiss citizens pay 28 percent, and the Chinese pay 32 percent, while American pay 11 percent – and only two countries' citizens pay less — Luxembourg and France, IBD writes.

Nor does any other country rely entirely on government spending, as Sanders and other Democrats propose. For example, 70 percent of Canada's health costs are government-financed, with 15 percent paid by private insurers and the rest paid out of pocket, In the U.S., the split is 49 percent government and 40 percent private insurance.

"What this shows is that the single-payer proposal offered by Sanders is extreme even by the standards of the socialist countries he admires," IBN writes. "The fact that leading Democrats are now backing a health plan that has never been tried — outside of, perhaps, Cuba — shows that they are either shamefully ignorant of how other countries finance their health care systems, or they are being purposely deceitful about how radical their plans really are."