Analysis by Gregory Krieg, CNN

(CNN) -- When Sen. Bernie Sanders hit the road in July to gin up resistance against Republican efforts to raze Obamacare, he delivered a two-part message: First, protect the current law. Second, push on and make the case for a single-payer system, or "Medicare for all."

This past weekend, at the Democratic Socialists of America national convention in Chicago, delegates and observers buzzed about that budding campaign to organize and rally for single-payer legislation on the federal level.

Those discussions were a break from the mainstream discourse on health care right now, which tends to fixate, appropriately enough, on how the GOP's "repeal and replace" pledge failed, the fixes required to sustain the Affordable Care Act, or the contours of Sanders' forthcoming "Medicare for all" legislation.

But there is an additional dimension on the left, which increasingly views health care policy as a beachhead -- one they are now well-positioned to capture -- from which to launch a wider effort to promote socialist ideas to more diverse audiences. What's feasible or not, in the current climate, and how to tinker with the equation, is essentially beside the point.

"We chose that issue for a reason: it will help mostly working people and marginalized people more than everyone else," DSA's Jess Dervin-Ackerman, an organizer with DSA East Bay chapter in Northern California, told me at this past weekend's convention. Her colleague, Jeremy Gong, tagged it to abortion rights, saying, "This is an economic issue in addition to an issue of gender. We need to create a universal, single-payer health care system that guarantees abortion access to all women, everywhere, with no questions asked."

Health care is where the grassroots energy is, organizers in Chicago agreed, and for new recruits the hard work of canvassing is brightened by the opportunity to sing the singler-payer gospel. The resulting surge in recruitment, Dervin-Ackerman said, has the knock-on effect of getting activists off social media, an often unproductively exhausting medium, and plugged in to their actual communities.

On the broader left, taking into account Democrats of all stripes, single-payer is increasingly popular. A recent Pew survey found 52% support for the policy among Democrats, a nearly 20-point spike in a little more than three years. The number jumps to 64% when narrowed to self-described liberal Democrats.

The outlook is much less rosy when Republicans are thrown into the mix. Nationally, only 33% support single-payer. But that number is 12 points higher than in 2014 and approximately three in five Americans, across partisan lines, now say the federal government should be responsible for "ensuring health care coverage for all Americans."

But as gun control activists are keenly aware, it takes more than positive polling to drive legislation. The reality of national politics today, in which Democrats are out of power and on the defensive in Washington, means that single-payer is a nonstarter in the House and Senate. Even then, top officials on Capitol Hill remain cautious. Senate Minority Leader Chuck Schumer only recently conceded the policy was "on the table," while Nancy Pelosi, his counterpart in the House, has been less willing, even rhetorically, to entertain it.

The left, though, is seizing on that lack of direction -- and a diminished incentive for the party to act given its inability to move legislation -- by working to make health care the defining issue in Democratic politics. The absence of actionable legislation also provides space for litmus testing potential allies. Potential 2020 primary candidates are facing them, along with party leadership up and down the midterm ballot, from city council candidates to gubernatorial and congressional hopefuls.

Most politicians are, of course, constitutionally uncomfortable offering categorical answers to yes-or-no questions, especially when the queries center on issues that can divide public opinion. The Democratic Party establishment is currently mired in a fight over whether support for abortion rights should be a litmus test for potential candidates. Unsurprisingly, party leaders with a mandate to win back power oppose it. California's lame duck governor, Jerry Brown, in an appearance Sunday on NBC's "Meet the Press," made an appeal for Democrats to open their ranks.

"The litmus test should be intelligence, caring about, as Harry Truman or Roosevelt used to call it, the common man," Brown said. "We're not going to get everybody on board. And I'm sorry but running in San Francisco is not like running in Tulare County or Modoc, California, much less Mobile, Alabama."

But the left is betting that, at this early stage, single payer -- as an overarching priority if not a singular concern -- represents the best vehicle to proactively address all those issues in vast swaths of the country historically unwelcoming to mainstream liberals.

"Every social and economic crisis presents in the hospital," said Bonnie Castillo, health and safety director for National Nurses United, the first national union to back Sanders' 2016 primary run. "Nurses care every day for people harmed by environmental pollution, climate change, the opioid epidemic, malnutrition, homelessness, joblessness, inadequate mental healthcare services. Health impacts everything, (which is) exactly why Medicare for all should be a priority for every Democrat."

The message is resonating with elected officials, like California Rep. Ro Khanna, a pro-Sanders Democrat from Silicon Valley who supported policy during his insurgent run in 2016. Speaking on Tuesday, he framed single-payer as a job-creating mechanism.

"There are a lot of entrepreneurs and tech leaders who say their biggest disadvantage competitively is the cost of health care. It's not tax policy, it's not wages, it's health care costs," Khanna said. "So you have the moral argument for it, but it's also something that you can get business leaders and technology leaders excited about."