Remember when endorsing M4A was an election loser?
Yeh, about that.

It's common sense: Democratic politicians who support "radical" notions like Medicare for All, free college, or preserving a habitable planet via a Green New Deal guarantee their own defeat....
It may be common sense, but it's wrong. Every single Congressional co-sponsor of the "Medicare for All" bills in the House and Senate who were up for reelection beat their Republican opponents in 2020. And in 2018. And in 2016. And every Democrat who lost reelection to a Republican had campaigned on the "boring, moderate" platform that Shor contends is the formula for success.

In fact, you have to go back a full decade to find a single Democratic incumbent who co-sponsored a Medicare for All bill and lost their reelection bid. One lost in 2010, when 52 total House Democrats lost reelection in the Republican blowout. For the entire period from 2002 to 2020, there were two. During that time Medicare for All has had between 38 and 124 co-sponsors in the House.
...we identified the 147 Congressional swing districts which flipped from Republican to Democrat in a House election in 2002 or later. We then looked at which of those Democrats won reelection the next time around, comparing the 12 Democrats from those districts who became co-sponsors of Medicare for All with the 135 "moderates" who did not support the bill.

All 12 Medicare for All sponsors won reelection, despite the fact that their seats had been held by Republicans just two years before. On the other hand, 30% (40 out of 135) of the moderates lost re-election in the next cycle.

Imagine that. People support M4A. Who would have guessed.
But how are you gonna pay for it, amirite?

Last week, the Congressional Budget Office (CBO) released an estimate of the cost of implementing a single-payer health insurance program in the United States. The CBO’s report is more exhaustive than any other recent study on the subject and concludes that replacing our current system with a single-payer system would insure every American while reducing overall health spending in the country...
The CBO answered these questions for four different single-payer designs and found that a single-payer system would save $42 billion to $743 billion in 2030 alone.
The CBO option that most closely approximates current Medicare for All proposals is Option 3, which features low payment rates and low cost-sharing. That option produces $650 billion of savings in 2030. Adding LTSS to that option, which also approximates what many current Medicare for All proposals do, looks like it would bring the savings down to around $300 billion.

So there are no downsides to M4A.