In nearly 800 days , a Democratic president and Congress may take office.

This is not as far away as it sounds. If Democrats want the chance to pass health reforms that will build on the Affordable Care Act and fix its defects, they need to start planning now.

The Democrats’ House victories in the midterms are an important step in that direction. Medicaid will expand in Idaho, Nebraska and Utah, thanks to ballot initiatives, and could expand in Kansas, Maine and Wisconsin, thanks to those states’ new Democratic governors-elect. Although Republicans picked up Senate seats, the 2020 and 2022 Senate maps still allow the possibility of a workable Democratic majority. Democrats must be ready. The process of writing the A.C.A. began years before it passed. Democratic legislators, activists and policy experts should be talking right now about how to build on it.

We already know a few things about what workable and worthy legislation will look like. First, it will be a straight Democratic bill. As Republicans did in 2017 on health care and taxes, Democrats will proceed unilaterally. Unlike Republicans, Democrats should put in the hard work to create a smart bill they actually intend to pass, one that commands broad public support.

Many Americans would prefer greater bipartisanship. So would I. But Democrats tried that, and look what happened. The A.C.A. was a good-faith effort to create a fiscally disciplined, ideologically moderate, market-based path to near-universal coverage. Max Baucus and other Democratic senators spent months fruitlessly negotiating with Republicans, who, it is obvious in retrospect, were cynically stalling. Republicans’ scorched-earth opposition to President Barack Obama and health care reform — not to mention the Trump presidency — have weakened the possibility that Democrats will do the same next time around.