If you’ve successfully landed on the beaches, but your forces are still taking heavy fire, what do you do? Do you concentrate on trying to hold the line and make further advances or do you sit in a circle and design a better landing craft?

The problem with Bernie Sanders’ health care vision isn’t the vision. His raw outline for a greatly simplified and less expensive health-care system is excellent in theory. The problem is the politics — the reality of which battle-scarred Hillary Clinton clearly has the better grasp.

This was the message Clinton tried to convey in the Sunday Democratic debate. Her most potent point on health-care reform centered on recalling the “public option” fiasco during the fight for the Affordable Care Act.

The public option was to be a government-run health plan competing with the private offerings in the health-care exchanges. It was a no-brainer to keep the insurance companies on a shorter leash. But, as Clinton noted, “even when the Democrats were in charge of the Congress, we couldn’t get the votes for that.”

Thomas E. McDonough, a health policy expert at Harvard, has also been through the health-care wars. As a Massachusetts state legislator, McDonough led an unsuccessful campaign to bring single-payer to his liberal state. In a recent New England Journal of Medicine article, he explained why a similar effort in Sanders’ own state of Vermont failed.

Vermont was the great hope for we fans of single-payer. (I was waving pompoms.) The state is progressive and one footstep from Canada. Gov. Peter Shumlin was totally onboard. He spent four years trying to make a single-payer plan happen. Three major-league studies showed that it was economically feasible.

But even in Vermont, a clear public mandate for single payer never materialized. A rebellion against it almost cost Shumlin the governor’s job.

Asked about this on Sunday, Sanders took a swipe at Shumlin (who has endorsed Clinton).

“Let me just say that you might want to ask the governor of the state of Vermont why he could not do it,” Sanders responded. “I’m not the governor. I’m the senator from the state of Vermont.”

Yes, and as senator from Vermont, Sanders introduced several single-payer bills that went nowhere. The most recent one, the 2013 American Health Security Act, attracted not a single co-sponsor.

The plan Sanders released two hours before the debate remains too sketchy for a reliable independent analysis, according to McDonough. But lack of detail isn’t his biggest concern. It’s opening a new front in the battle to defend Obamacare.

“Republicans sent a bill to the President’s desk last week that would eliminate health insurance for 22 million Americans by 2018,” McDonough wrote me. “This is not beanbag. It’s the real deal, and we have to focus where it matters the most.”

“Bernie wants to lead us on a distraction tour while Republicans want to kill the progress we have made.”

How far have we come? Thanks to Obamacare, almost 18 million formerly uninsured Americans now have health coverage. A report just out of Georgetown University has the rate of uninsured Hispanic children falling to a historic low.

Insurers can no longer turn down people with pre-existing conditions. And important politically, Obamacare has demonstrated that universal coverage is doable without creating mass unemployment or “exploding” deficits. On the contrary.

Making Obamacare more Medicare-like through incremental steps may not feed the romantic urge to reinvent health-care reform from scratch, but there’s no other road, not in the America of 2016. Finally, let’s not forget that vanguard of reform is still on the beaches and taking fire.

Froma Harrop is a syndicated columnist. Follow her on Twitter @FromaHarrop. She can be reached by email at: fharrop@gmail.com.