I think Paul Waldman is right to express doubt about this widely held notion about the Affordable Care Act:
... a belief that the ACA's failure would make single-payer more likely fundamentally misreads our political history.And how did we arrive at one of those necessary preconditions -- "the momentary possession of big enough congressional majorities to overcome Republican obstruction"? We got there because the presidency of George W. Bush was a miserable failure on so many levels, and because Bush did next to nothing to try to right his own ship, with the result that his failings empowered Democrats in 2006 and 2008. Don't hold your breath waiting for that kind of cluelessness to come along again.
... Would it then be possible to assemble the kind of political momentum necessary to pass single-payer? That seems all but impossible. Keep in mind that meaningful health insurance reform had behind it an almost unanimous Democratic party for decades before it was finally achieved. What it finally took was a worsening of key trends like premium costs and rates of uninsurance, combined with the momentary possession of big enough congressional majorities to overcome Republican obstruction, combined with the co-opting of the powerful interests that traditionally opposed reform....
The other postwar Democratic president who was able to extend the social safety net significantly was Lyndon Johnson -- and why was that possible? It was possible because he'd finished the term of an assassinated president who'd become a demigod in death, and then he defeated a Republican regarded as so extreme that the center utterly abandoned the GOP. A series of events like that could empower Democrats to enact Medicare for All, but it's not one I'd wish on America.
In the past, this has worked for Republicans as well -- gas lines, double-digit inflation, and the Iranian hostage crisis (and failed rescue mission) in the Carter years empowered Ronald Reagan in the 1980s. But I think it would be a lot easier now for Republicans to make drastic changes -- they're more organized, their voters don't expect them to embody whatever the Establishment regards as centrism, and the radical changes they'd seek would be just fine with big business.
Democrats need a confluence of extraordinary circumstances in order to make big societal changes. They may not get them again for quite some time.