The way the Democratic candidates talk about "Medicare for All" has shifted and sharpened over the course of the campaign — and Medicare for All has gotten less popular in the process.

The state of play: When Sen. Bernie Sanders introduced his "Medicare for All" bill in 2017, all of his likely 2020 rivals in the Senate signed on as cosponsors, and many Democrats treated Medicare for All as a catch-all or a loosely defined goal.

New polling from the Kaiser Family Foundation and the Cook Political Report confirms that while Democratic voters like the idea of “Medicare for All,” it would be a risk in a general election.

Between the lines: This poll was conducted in the formerly “blue wall” states of Pennsylvania, Minnesota, Michigan, and Wisconsin.

Sen. Elizabeth Warren's two-part plan to pass a public option as a transition into Medicare for All — and then full-blown Medicare for All a few years later — has revealed the difficulty of appealing to both the pragmatic and progressive wings of the party.

The big picture: Warren's already being criticized by progressives for not being a Medicare for All purist, and because of the realities of governing, they may have a point: Passing two major health reforms in one term is unheard of.

Sen. Elizabeth Warren's presidential campaign on Friday unveiled what would be her roadmap for overhauling the country's health care system if elected, carving out an initial public option with the promise of implementing 'Medicare for All' within her first three years in office.

Why it matters: The plan gives Warren a defense against criticism that she would abruptly strip away Americans' ability to choose their care and force them off private insurance.

Former Secretary of State Hillary Clinton said during the DealBook conference in New York on Wednesday she doesn't believe 2020 candidate Sen. Elizabeth Warren's Medicare for All plan would ever be enacted.

"The smarter approach is to build on what we have; a public option is something I've been in favor of for a very long time. I don't believe we should be in the midst of a big disruption while we are trying to get to 100% coverage and deal with costs."

Public support for Medicare for All might have peaked, but it’s still a powerful idea among many Democrats.

By the numbers: Support for the national health plan rose from around 40% in 2000 to a high of 59% in March of 2018, but had slipped back to 51% by October of this year.

Sen. Elizabeth Warren's Medicare for All plan takes on every major health care industry — insurers, doctors, hospitals and drug companies — in her pursuit of expanding coverage and lowering costs for the middle class.

Why it matters: We've never tried any cost containment measures that are remotely close to being as aggressive as Warren's, and there could be consequences if payment rates are slashed so low.

Sen. Bernie Sanders defended his Medicare for All plan on the campaign trail in Iowa, telling ABC News that it's "much more progressive in terms of protecting the financial well being of middle income families" than Sen. Elizabeth Warren's plan, which she unveiled last week.

Why it matters: Warren has frequently said she's "with Bernie" on Medicare for All, but the health care truce between two of the most progressive candidates in the race seemingly broke with Warren's newly released plan.

House Speaker Nancy Pelosi told Bloomberg on Friday she isn't a "big fan" of Medicare for All, calling the program "expensive."

Why it matters: The comments came the same day presidential candidate Sen. Elizabeth Warren unveiled her proposal to pay for a Medicare-for-All program. Other candidates, like Sen. Bernie Sanders and Julian Castro also support the principle.

Sen. Elizabeth Warren has released her long-awaited plan to pay for "Medicare for All," which she says will put the $11 trillion that would be spent out-of-pocket on health care over 10 years "back in the pockets of American families."

The bottom line: This will be paid for "with targeted spending cuts, new taxes on giant corporations and the richest 1% of Americans, and by cracking down on tax evasion and fraud. Not one penny in middle-class tax increases," the plan states.