I'm all for single payer / Medicare for All (etc.) but the timing of your strategy is askew. Let's say that "advocating passionately for Medicare for All" won't result in a net loss of votes for Biden, and that he gets elected. (I think it's unlikely that not advocating for M4A will be the tipping point that results in a loss for Biden, but I suppose that's hypothetically possible.) Let's also speculate Biden gets elected and that enough Republicans support this agenda so that it can pass Congressional review (and won't be overturned in the Supreme Court, which is in itself a possibility).

Enacting M4A could easily take two years (by Elizabeth Warren's estimate), which means even more people will have lost their employer-sponsored health insurance, and people who do regain full-time jobs with insurance will probably not be covered for pre-existing conditions. Nor will this M4A pay retroactively for all the expenses incurred before it took effect.

If Biden comes out for M4A without a plan for helping families who are suffering now, then he will be just another politician with a pie-in-the-sky solution.

The number of people suffering from losing employer-sponsored health insurance is a powerful argument for single payer, but it's too late for single payer to help those people.

If we have to triage, the humane approach would be to provide some care / respite / debt relief for the uninsured, protect Obamacare from further weakening, and then (and ONLY THEN), with all the energy and resources we have "advocate passionately for Medicare for All.”

This two-stage approach is a compromise, a stop-gap, a delay, but without it, who will trust any politician who promises Medicare for All as the solution?