Democrats are increasingly embracing "Medicare for All." Thing is, though, they don't necessarily agree about what that means.

Why it matters: Democrats haven't had to reconcile these competing visions ahead of the midterm elections, when the sheer number of candidates running for different offices has allowed everyone to stick to their own definition of a broadly popular term.

But that will surely change once the 2020 primary gets started.

The options range from full-scale single-payer to a far more modest, optional expansion.

Sen. Bernie Sanders' "Medicare for All" bill would immediately establish a single source of health care coverage, for all services, with no cost-sharing. It's the most aggressive proposal out there, and is significantly more robust than the existing Medicare program, or even Canada's single-payer system.

The Center for American Progress' version wouldn't immediately move everyone into a new system. People could choose to opt into a new, beefed-up version of Medicare. But newborns would be enrolled automatically, so private insurance's days would likely be numbered.

There are several other versions of a Medicare buy-in. The most limited would only apply to individuals over a certain age. The next step would be all individuals. The step after that, as proposed by Sen. Chris Murphy, would also allow employers to buy into a beefed-up version of Medicare as their health care plan.

The details: How much each plan would cost will depend on how each one is structured. Broadly, the more people it covers and the more services it provides, the more it will cost.

Sanders' bill would be the most expensive on this list, though estimates place its total price tag roughly in line with what we're expected to spend under the status quo. It would require substantial tax increases to replace costs that are now borne through premiums and out-of-pocket spending.

What's next: Most of Democrats' leading 2020 prospects in the Senate have signed on to Sanders' bill, but I'd expect many of them to treat it as a jumping-off point or a notional embrace, and to continue coming up with their own, separate policy proposals.