Sen. Bernie Sanders (I-VT) speaks during a health care rally at the 2017 Convention of the California Nurses Association/National Nurses Organizing Committee in San Francisco. Justin Sullivan | Getty Images

Some Democrats threatened to block the Affordable Care Act over a Medicare opt-in in 2009. A decade later, the same public option looks like a small step for a Democratic Party that has embraced sweeping change on health care as it looks to recapture the White House. A party buoyed by resistance to recent GOP efforts to repeal the law known as Obamacare will now have to decide how far to move toward insuring all Americans as they try to defeat President Donald Trump next year. Democratic presidential candidates agree they want universal health coverage. They only differ on how to get there — and on which plan can earn enough support nationwide. Sen. Bernie Sanders of Vermont has called for a transition to a universal "Medicare-for-all" system. Hopefuls including Sens. Elizabeth Warren, D-Mass., and Kamala Harris, D-Calif., endorsed a bill he introduced in the Senate to move to government-run universal health coverage. Other Democrats think such a proposal would move too far, too quickly. Amy Klobuchar — a Minnesota Democrat seen as one of the more centrist 2020 primary candidates — has floated a public option to allow consumers to choose whether to buy into a government-run plan. Sen. Sherrod Brown, an Ohio Democrat who opted not to make a presidential bid after considering one, wants instead to lower the Medicare eligibility age to 55 from 65. Sen. The fact that Democrats broadly view a public option as a more incremental step shows just how much the health- care debate has moved in recent years. After all, Democrats spent most of a decade taking a political beating over the Affordable Care Act, then flipped control of the House last year after Republicans got their first real chance to repeal it. Former Montana Sen. Max Baucus illustrates the party's shift. As Senate Finance Committee chairman, he helped to torpedo the public option in 2009, earning the ire of liberals. His tune changed by 2017. Baucus told NBC News that "the time has come" to consider single-payer government health care. The differences on health care in the Democratic primaries essentially come down to how dramatically to build out the public Medicare and Medicaid programs: Cover all Americans in one bold stroke, justifying significant tax increases in the name of lower costs, or expand coverage more slowly, through a plan that Americans seem more ready to digest? "All of these candidates support a wide range of proposals that would move toward universal coverage and create at least an option for public coverage," said Larry Levitt, senior vice president for health reform at the Kaiser Family Foundation. "The Democratic candidates differ more in how quickly they want to move and what's immediately possible politically than what the end goal is." Yet, despite the primary candidates' differences, Levitt believes not as wide of a gulf exists between them as many would perceive.

How the Democrats' plans differ

Sen. Elizabeth Warren, D-Mass., speaks during Sen. Bernie Sanders' event to introduce the Medicare for All Act of 2017 on Wednesday, Sept. 13, 2017. Bill Clark | CQ-Roll Call Group | Getty Images

The question of what Democrats think they can or should achieve on health care will help to define the race to take on Trump. And pressure is on for Washington to do something about health costs: The average annual premium for an employer-based plan rose 5 percent in 2018, while prescription drug costs have steadily climbed. Major 2020 Democratic candidates agree they want at least a public option. Any disagreements surround how much further to go. While such an opt-in proposal could take various forms, it would generally allow people who do not have employer-sponsored insurance or do not qualify for ACA subsidies to buy a government plan through either Medicare or Medicaid. Proponents see the potential for both more affordable and more widely available coverage, especially for Americans living in areas where insurers dropped out of Obamacare. A bill reintroduced last month by Sen. Brian Schatz, D-Hawaii, offers one example. It would let states create a program for residents with any income to buy into a Medicaid insurance plan. The federal and state Medicaid system, which 36 states and the District of Columbia chose to expand under Obamacare, currently offers coverage to low-income Americans. Every senator already running in 2020, as well as Brown, has co-sponsored Schatz's legislation. Sanders on the field's left wing and Klobuchar in the group's more centrist lane have backed it. "What we should be doing is some immediate fixes, which is reinsurance cost sharing, but then go into a public option, something that President Obama wanted to see when he passed the Affordable Care Act," Klobuchar told MSNBC on Tuesday. "You can do it by expanding Medicaid, you can do it by expanding Medicare."

Sen. Amy Klobuchar (D-MN) announces her 2020 presidential bid on February 10, 2019 in Minneapolis, Minnesota. Stephen Maturen | Getty Images

A Medicaid buy-in has overwhelming public support: Three-quarters of respondents to a Kaiser Family Foundation poll in January said they favored "allowing people who don't get health insurance at work to buy health insurance through the state Medicaid program," versus only 18 percent who said they opposed it. But many Democrats want more ambitious action. Sanders, who helped to bring single-payer more into the political mainstream during his 2016 presidential bid, has said a more drastic overhaul is "what we must do to end the international disgrace of being the only major country not to make health care a right." Sanders Medicare tweet So how would "Medicare-for-all" differ from a public option? A bill proposed by Sanders would insure all Americans after a four-year transition period, rather than offer an option to those not covered by employer-sponsored plans. It would include not only primary and preventive care, but also prescription drug, mental health, substance abuse dental and vision coverage. Harris, Warren and Sens. Cory Booker of New Jersey and Kirsten Gillibrand of New York — but not Klobuchar and Brown — signed on to Sanders' legislation in 2017. Support for "Medicare-for-all" goes well beyond 2020 contenders, though. More than 100 Democratic House members signed on to a single-payer bill unveiled last month by Rep. Pramila Jayapal, D-Wash. It would move to universal coverage in two years, taking about half the time of Sanders' plan.

Democratic leaders keep their distance

Fifty-six percent of Americans support "Medicare-for-all," while 42 percent oppose it, according to Kaiser polling from January. But support wavers when Americans are told about two potential effects of such a system: higher taxes for most Americans or the elimination of private insurance companies. Democratic leaders have had to grapple with those possible political consequences ahead of the 2020 elections. Democrats not only want to deny Trump a second term, but also hold House seats in ideologically split areas that propelled the party to control of the chamber in November.

Republicans have slammed "Medicare-for-all" as they allege Democrats have drifted toward socialism. They have in particular targeted the potential cost of a government-run system and the tax increases that would likely come with it. Some groups estimate Sanders' plan would cost the federal government roughly $30 trillion — a staggering figure but about the same as total projected U.S. health-care spending, according to Vox. Critics also argue that people are wary of getting rid of their current private or employer-sponsored plans. In a statement when Jayapal unveiled her legislation, National Republican Congressional Committee spokesman Michael McAdams wished "good luck to the vulnerable House Democrats who will be forced to defend this $32 trillion boondoggle." House Speaker Nancy Pelosi has showed skepticism of "Medicare-for-all" as she tries to maintain a House majority. In a Rolling Stone interview published last week, she asked in part: "How's it gonna be paid for?" The California Democrat noted that she "wanted to have a public option" as part of the ACA when the House passed it in 2009 during her first stint as speaker. But "we couldn't get that through the Senate," she said. Democrats could find it difficult to take steps to beef up Medicare and Medicaid, even if they win the White House next year. To pass a president's health-care plan, they would likely need to flip control of a Senate where Republicans currently hold 53 of 100 seats. Even then, it would take deft political maneuvering to get the whole Democratic caucus united behind a plan. The medical industry, which opposed the GOP Obamacare repeal plans, will also likely offer resistance to "Medicare-for-all" or a Medicare public option. The American Medical Association, the nation's largest association of physicians, said it backs fixes that increase coverage and reduce costs within the current insurance structure. The group said it opposes "Medicare-for-all" based on what it calls a "mountain of evidence" about high costs and the potential to disrupt innovation and quality of care. The AMA also criticized a Medicare public option, expressing doubts about its solvency and potential damage to the private market.

How we got here

Activists marched to the offices of Senators Schumer and Gillibrand in New York City on September 5, 2017; carrying a giant lunchbox filled with messages from constituents that urged them to get Back To Work and Save Our Healthcare. Erik McGregor | LightRocket | Getty Images