In the heat of the 2016 Democratic primary, Bernie Sanders released one of his signature proposals: Medicare-for-All. In response, economists, policy experts, and the liberal media all hammered the plan: Vox’s Ezra Klein called it “puppies-and-rainbows” and Paul Krugman wrote at The New York Times that “Sanders ended up delivering mostly smoke and mirrors.” The Urban Institute released an analysis that contended that Sanders’s proposal would have cost twice what the campaign had projected. Sanders’s plan was dragged for being vague, unrealistic, and light on the nuts and bolts.

Now, Sanders is gearing up for another go. Following the latest death of the zombie-like Trumpcare, he has stated that he will introduce single-payer legislation to the Senate. A lot is riding on the hope that Sanders’s new bill will be a robust piece of legislation. The political landscape has changed drastically since 2016, with progressives demanding more radical action to shore up and build upon the gains made by Obamacare. Among Democrats, support for single-payer has increased by 19 percentage points over the past three years. And for the first time in history, a majority of Democrats in the House have signed on as co-sponsors to Representative John Conyers’s Medicare-for-All bill.

But it’s hard to deny that single-payer is an area where progressive politics has outstripped policy. Conyers’s bill is largely seen as a symbolic piece of legislation, and not only because Democrats would first have to win back Congress and the White House to even begin passing it. As Joshua Holland wrote on Wednesday in The Nation, the momentum for single-payer is “tempered by the fact that the activist left, which has a ton of energy at the moment, has for the most part failed to grapple with the difficulties of transitioning to a single-payer system.”

We have seen this dynamic play out in real time in California, where the country’s most promising single-payer bill floundered on the details of the legislation. And on a national level, there is little clarity around an actual plan with comprehensive steps to genuine universal coverage. For a party that prides itself on being the country’s only rational, empirical party, where are the Democrats’ famed wonks on single-payer?

It’s hard to deny that single-payer is an area where progressive politics has outstripped policy.

As Harold Pollack, a health policy researcher at the University of Chicago, told Holland, “There has not yet been a detailed, single-payer bill that’s laid out the transitional issues about how to get from here to there. We’ve never actually seen that. Even if you believe everything people say about the cost savings that would result, there are still so many detailed questions about how we should finance this, how we can deal with the shock to the system, and so on.”