Elizabeth Warren made sure to specially thank South Carolina Rep. James Clyburn when they introduced their student debt forgiveness plan this week.

The reason: He might actually get a vote on it.

"I am deeply grateful to the congressman for taking this first piece on student debt cancellation so that we have a chance to work it through the House. Right now, we're not likely to get a vote in the Senate," she said, to chuckles in the audience.

"But [we] have a chance to work it through the House so we can iron out any kinks and get it ready to go so that soon, I hope, we have people in the House and the Senate who are interested in passing this and we have someone in the White House who will sign it into law," the Massachusetts senator added.

She's not wrong to hope, but then, this scenario represents an uphill climb for her party. Even if Democrats win the White House and hold onto the House next year, winning the Senate already looks tough.

And even then, to pass some of their most ambitious proposals, Democrats would either need a filibuster-proof majority (60 senators) or to blow up the filibuster altogether, which it's not clear that all Democratic senators would want to do.

All of which raises a tough, basic question: If a policy just doesn't seem viable even if a candidate wins, what does the debate accomplish?

"Priming" the issues

It's not just student debt cancellation; Democrats have discussed a wide variety of potential policies that would be hard to pass, even with a majority in the Senate: Reparations for slavery, the Green New Deal, expanding the Supreme Court and "Medicare for All" are dramatic proposals that appear to have very difficult paths to passage. Even a less-drastic proposal, like a public option for health insurance, could be a stretch.

Medicare for All, as presented by lawmakers like Vermont Sen. Bernie Sanders, is maybe the highest-profile example in this primary of a hyperambitious plan — not only would it be an overhaul of the U.S. healthcare system, but also it would go further than even many existing single-payer systems around the world, as Sarah Kliff has reported at Vox.

And it would have a tough time of passing. Sanders has said he would try to pass it via reconciliation, which only requires a simple majority of 51 senators. But even if he could, and even if Democrats had 51 senators after 2020, getting those votes would be a stretch considering that an array of current Democratic senators oppose Medicare for All to some degree.

It is still true, however, that debating it now doesn't do nothing. Politicians like Sanders and Warren may recognize that even if their policies don't pass in their respective (hypothetical) presidencies, talking about the policy now could lay the groundwork for Medicare for All in the future.

"The campaign does serve the purpose of priming people or helping them to understand the contours of the debate so that when you get to the time that you're actually trying to pass legislation, people have already had exposure to the issues at play," said Lanhee Chen, who was policy director on the 2012 Mitt Romney campaign.

It also could open the Overton window — the range of policies that that are considered realistic ideas — wider, in the process making it more likely that a smaller — but still major — change could happen in the nearer term.

"I think that a very legitimate reason for why a candidate would propose a bold health care plan like Medicare for All, even if they're not going to be president or if they can't get it passed is, over the long term, it moves public opinion and political will in your favor and it may be easier to have something like public option," said Jennifer Palmieri, director of communications on Hillary Clinton's 2016 presidential campaign.

All of this debate comes at a price, however, says Robert Blendon, professor at Harvard's T.H. Chan School of Public Health. He believes that talking this much about Medicare for All takes oxygen away from other related issues that voters care about more — and that might have more of a shot at seeing bipartisan changes.

"You give them a list and you discover that they're actually not talking about Medicare for All or a redo of the Affordable Care Act," he said. "They're focused on their own pocketbook issues: high drug costs, charges by hospitals and insurance premiums. And they're not concerned about overall spending."

It's true that Medicare for All proponents argue that their plan would tackle all of these problems. One of their challenges, then, is convincing voters that a wholesale overhaul of the system is the right fix.

Never say never

It's not that pushing bold ideas is an entirely calculated, cynical move — candidates have ideas they believe in, even if those ideas don't seem to have much of a path to reality.

On that note, there's one important caveat: Programs are impossible to pass until they're not. That shift can happen relatively quickly.

"John F. Kennedy ran in 1960, and Medicare for retirees was one of his lead issues," Blendon says. "He wins and the leaders from the House and Senate meet with him and tell him that's in no way possible."

But then, after Kennedy was assassinated and President Lyndon Johnson took office, a couple short years passed, and Congress swung hard toward more liberal Democrats.

"Lyndon Johnson meets with the same leaders and they say, 'Lyndon, we can pass the Medicare bill,' " Blendon said. "For a big change to occur, you would have to have a change in the president and their leanings and the Congress. But that happens every now and then."

What candidates get out of it

But from a calculated political point of view, there's also a lot to gain from talking about these sorts of big, ambitious policies — for one thing, even if ideas like Medicare for All aren't popular with the total electorate, they are often much more popular with Democratic primary voters.

In addition, putting bold ideas out there can help a candidate tell a particular story about themselves.

"It tells voters that you think you get the depth of the problem," Palmieri said. "And it tells voters that your inclination is to have a very bold solution, and well beyond the policy, that tells voters something about the kind of person you are."

For example: Talking about Medicare for All helps Sanders reinforce that he wants to remake government — as he put it at the start of a recent speech on the policy: "While we're at it, let's make a political revolution.

Warren, similarly, has rolled out plan after plan — which has helped her craft an identity as the detailed policy thinker of the pack.

On the flip side, former Vice President Joe Biden is also using Medicare for All to distinguish himself, as he appears to be readying himself to weaponize California Sen. Kamala Harris' support for the policy against her in next week's debates.

Having a list of bold ideas can also be necessary for candidates who are Congress members in a time of gridlock.

"If you're a senator or a member of Congress and you were running for president, you're probably not going to have much of a legislative accomplishment record to run on because Congress has been so dysfunctional," Palmieri says. "So the manner by which you distinguish yourself is a very bold policy idea."

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