The Democrats won control of the House, largely on the back of health policy. And many members of the caucus have gone on record in favor of what’s come to be known as “Medicare for all.”

The idea is hugely popular, backed by 58 percent of Americans in some polls and up to 70 percent in others. But what does that really mean? And is there a chance that such an idea will become law any time soon?

The last question is the easiest to answer; No. As long as Republicans control the Senate, where they increased their majority on Tuesday, and as long as President Trump remains in the White House, there is zero chance that Americans under age 65 will get access to Medicare.

What is Medicare for all?

 But even answering the first question is complicated. It turns out that Medicare for all means many different things to different Democrats. Sometimes it doesn’t really mean Medicare. And it often doesn’t really mean for all.

Instead, the phrase has become short-hand for a wide range of ideas that really mean broader access to public insurance. But the design of that coverage is very different, depending on who you are talking to. The Kaiser Family Foundation has produced a very nice summary of the many plans here.

Start with the most far-reaching: Sen. Bernie Sanders (I-VT) plan to replace the entire health insurance system with a single public plan. No more employer-sponsored health coverage (which currently covers most Americans under age 65), no more Medicaid. No more ACA health exchanges for individuals. In fact, no more Medicare as we know it.  Just a single government payer for all Americans, no matter their age.

Then there is what was called the “public option” during the debate over the 2010 Affordable Care Act. A Medicare-like public plan would be offered on the ACA marketplace alongside private insurance. Individuals and, in some bills, even employers, could purchase coverage. While some backers use Medicare to frame these plans (they are sometimes called Medicare Part E or Medicare-X), they really are not Medicare at all. Their benefits would be different and so would their premiums.

The third variation on the theme, which harkens back at least to the Bill Clinton Administration, is a Medicare buy-in. Unlike the other ideas, this really is Medicare—just made available starting at, say, age 50 or 55. Like today’s Medicare beneficiaries, enrollees could choose traditional Medicare, Medicare supplemental (Medigap) coverage, Part D drug coverage, or Medicare Advantage managed care. Unlike, the over-65 enrollees, younger buyers would pay premiums that would cover the full cost of benefits.

What will Democrats do?

My Urban Institute colleagues have estimated that a Sanders-like plan would increase public costs by $32 trillion over 10 years. We don’t know what the other ideas would cost, but presumably it would be much less.

Because health care coverage, especially for those with pre-existing conditions, was such an important campaign issue, House Democrats will have to do something once they gain control of the chamber in January. But what?

The most likely bill is something to protect the ACA from the Trump Administration’s regulatory efforts to dismantle it and the multiple state legal challenges that put it at risk. Even Senate Majority Leader Mitch McConnell says he is willing to work with Democrats to fix the ACA, though his definition of fix and theirs may differ.

But the ACA never promised true universal coverage. Including its expansion of Medicaid (which not every state accepted), the ACA reduced the share of the unisured to about 12.7 percent before Trump began scaling it back (the uninsured rate has since risen to 15.5 percent).

The 2020 fight

House Democrats will also try to protect current Medicare from any administrative efforts by the Trump Administration to scale back benefits. At the same time, there is a chance, however remote, that they may find a work together with Trump to reduce Medicare drug costs.

But all of that falls far short of Medicare for all—no matter what you think it means.

So what will newly empowered House Democrats do? My best guess is that they pass a relatively modest buy-in bill. Then, it dies in the Senate. And everyone fights about it all over again in 2020.