A clamor to create “Medicare for All” has exploded on the left. Democratic presidential hopefuls are racing to co-sponsor legislation, rising stars in the party are embracing it, and national polls show Americans warming to the concept.

But even the idea’s most fervent backers acknowledge that the goal is far off in the distance, beyond the next year or even the 2020 election.

Their aim for now is to shift the health care debate. By making single-payer health care — a model under which all Americans would get their insurance from a single government plan — the progressive position, advocates argue that gives Democrats representing conservative areas of the country political cover to support more modest proposals to expand the government’s role in health insurance.