As we near November's midterm elections, Democrats haven't distilled one of their biggest talking points — Medicare for All — down to one single policy.

The big picture: The fight for universal health care is not a new one. But the wave of Democrats campaigning on "Medicare for All" represents the most mainstream political support the idea has had in decades.

How it started

President Truman first proposed a national health care program in 1945, and it remained a mainstream debate for decades. President Nixon even had a universal health care proposal — the Comprehensive Health Insurance Plan, or CHIP. (No relation to today's CHIP program for low-income children.)

• CHIP was a three-pronged plan that combined employer-based insurance, government assistance for low-income families, and Medicare for seniors. Participating in one of those programs would have been mandatory.
• But after the 70s, the campaign for universal coverage faded.

Fast forward to 2016, when Sen. Bernie Sanders' campaign thrust explicit calls for a single-payer system issue back into the national debate. In 2017 he introduced the Medicare for All Act with Sens. Cory Booker, Richard Blumenthal, Tammy Baldwin, Kamala Harris, and more as cosponsors.

• Sanders says on his website that Medicare for All is building "upon the success of the ACA to achieve the goal of universal health care."

Where we are now

Axios' Sam Baker reported that adopting Medicare for All has become something of "a litmus test for a lot of Democratic primaries in 2018."

• Democrats haven't decided on one message for what that will look like.
• But the majority of Democrats and Republicans all support the initiative, per a Reuters/Ipsos poll from last month.

Yes, but: Politico's Paul Demko reported in August that the idea hasn't been easy to sell to voters in the primaries.

• A veteran Democratic pollster, John Anzalone, told Politico: "Voters are smart enough to know that Medicare for all isn't going to happen right now, or maybe ever."

On the other side: A source familiar with President Trump's thinking on the issue told Axios' Jonathan Swan that a counter-message to Medicare for All "is the best performing message of...in this November's election."

The bottom line: The Democrats' fight has been a long time coming, and success in universal health care would be a major party victory. But first, they'll need to get their plan straight.