All of this is exactly why Warren's plan to enact M4A is superior to Bernie's. Warren is the only one being serious about all the hurdles you just mentioned.
I've said since last year that Warren's plans had more meat than Bernie's, but not sure why that would even be a factor in the primaries.
President sets the agenda, and unless the president has a specific plan he's pushing hard then it's Congress, not the White House, that writes the plan. Even when the White House does write a plan Congress goes ahead and fukks around with it something heavy before they get around to passing it. And who is in Congress....?
It reminds me of when Obama shyt on Clinton during the debates for wanting an individual mandate (because he thought forcing people to buy insurance didn't play well as a talking point), then turned around and included an individual mandate in the ACA. Did it matter who came up with it, or really what Obama's position on it was at all?
You vote for the candidate you trust to set the agenda, inspire the country forward, make good decisions in office, and have the integrity to stand by that agenda and not get on some other shyt. All the details get worked out between a few thousands voices of which 4/7 folk on the stage will be involved regardless of who wins.