Abortion was too controversial a litmus test for Democrats, so California Gov. Jerry Brown proposed that perhaps the party should instead just focus on listening to the "common man."

That too appears not to have gained traction among Democrats. So, Sen. Bernie Sanders (I-VT) has reportedly offered another ultimatum: single payer health care or else.

The Vermont senator himself has not explicitly said he’ll support primary challenges to those who won’t support his push for a so-called Medicare-for-all health care plan. But there are plenty of signs that Sanders and his allies view the issue as a defining moment for Democratic lawmakers. “Our view is that within the Democratic Party, this is fast-emerging as a litmus test,” said Ben Tulchin, the pollster for Sanders’ White House run.

If Democrats are confused as to exactly what Sanders has in mind for American health care, they can go to his official website.

Bernie’s plan would create a federally administered single-payer health care program. Universal single-payer health care means comprehensive coverage for all Americans. Bernie’s plan will cover the entire continuum of health care, from inpatient to outpatient care; preventive to emergency care; primary care to specialty care, including long-term and palliative care; vision, hearing and oral health care; mental health and substance abuse services; as well as prescription medications, medical equipment, supplies, diagnostics and treatments. Patients will be able to choose a health care provider without worrying about whether that provider is in-network and will be able to get the care they need without having to read any fine print or trying to figure out how they can afford the out-of-pocket costs.

Sanders perhaps feels emboldened to push the single payer plan after Republicans failed to repeal and replace Obamacare - multiple times. Yet, Politico expects the Vermont senator to face resistance from establishment Democrats as he prepares to embark on this "political revolution." Democrats may agree with Sanders on the merits of single payer, but they worry the policy could ruin their election chances.

In addition to failing to agree on their policy agenda, Democrats can't seem to identify a leader.