Vermont Sen. Bernard Sanders may want to be president, but he’s not yet serious about governing — or even about defending the hard-won gains of Obama-era Democrats.

The evidence: The single-payer health care plan he rushed to produce before Sunday’s Democratic debate in Charleston, S.C.

Sanders has as much chance of getting Congress to pay for his scheme as Donald Trump has of getting Mexico to pay for his wall. New York Times columnist Paul Krugman and The Atlantic’s Ta-Nehisi Coates, among others, have been critical of the plausibility of his approach.

It’s not just that a Republican Congress would never back his federally administered single-payer insurance proposal. Many Democrats wouldn’t go for the way he funds it, with massive tax increases on top earners, investment income and even middle-class families.

It was Democrats, led by Vice President Joseph R. Biden Jr. and Sen. Charles E. Schumer, the presumptive leader of the caucus after Sen. Harry Reid, who insisted on locking in Bush tax cuts on income below $450,000 — rather than below $250,000, as Sanders preferred — in a 2012 deal with Republicans.

But the problem for Sanders, and for Democrats, is much deeper than that. What should really alarm Democrats about the Sanders plan isn’t its detachment from political reality, but his desire to implement it.

If Sanders had a wand as magical as his read of American politics, he would eliminate the private insurance industry. That might not bring on a depression or a recession, but it would throw hundreds of thousands of Americans out of their jobs. Given the left’s antipathy toward insurance companies, perhaps some liberals would greet that as an acceptable loss in the name of a greater good of booting private insurers out of the health care system. But the economic disruption, exacerbated by a new 6.2 percent payroll tax on employers, is no small consideration.

Growth may not be a panacea, but, as we’ve seen in recent years, an economic tidal wave surely sinks all boats.

The sheer cost of Sanders’ proposal — $1.38 trillion per year (yes, trillion per year) or about 35 percent of the current budget — means he wouldn’t be able to spend on anything else. What taxes would he pile on top of the 52 percent top rate for investment and regular income to pay for other proposals?

Indeed, as The New York Times’s Upshot column pointed out earlier this week, it’s more of a tax platform than a health care proposal. 

There are still some details to be filled in, but folks making $250,000 or more would see their marginal federal income tax rates rise from between 33 percent and 39.6 percent to between 37 percent and 52 percent. At the same time, Sanders would raise taxes on investment income to the same higher rates as regular income. That might expand the middle class by redefining it downward, as many families who have earned, invested and saved would find it harder to put food on the table, buy homes and send their kids to college.

The predictable long-term result: a political revolution — away from liberalism.

In terms of the health care system, a Machiavellian Republican would cheer the arrival of Sanders’ plan on Capitol Hill. In fairness to Sanders, he would be repealing and replacing Obamacare with a version of the simplified single-payer system for which liberals have longed.

But the complexity of Obamacare has been one of its saving graces. Just ask Republicans, and the Supreme Court, how hard it is to come up with a way to eliminate Obamacare without disrupting the features that American voters like.

Moreover, Sanders is operating in a political environment in which leading lights of the GOP, most notably Speaker Paul D. Ryan, have been arguing to turn government-subsidized health care programs into a system of “premium supports” for the purchase of private insurance. 

It would be easier to transition from Sanders’s plan to Ryan’s plan than from Obamacare to Ryan’s plan. And it would certainly be easier to slash funding for one big Medicare-for-all plan than from the patchwork of government-subsidized insurance programs.

In that way, Sanders would provide a window for Ryan and congressional Republicans to rewrite his plan, attest to the virtues of the safety net, and try to implement their own version without increasing spending or taxes. 

Sanders’ appeal — much like that of Presidents Barack Obama and Ronald Reagan — is that his rhetoric is visionary. But unlike them, his substance is even more radical than his rhetoric. I suspect that if he wins the Democratic nomination, he’ll come under a lot of pressure from Democratic officials to revise his health and tax plans — both to spare them the wrath of voters and because they truly believe his plans would be deleterious.

But for now, Sanders’ proposal tells us a lot about his seriousness of purpose: Even if he could deliver on his promise — which he can’t — it would jeopardize government subsidies for health care by re-opening the current system, harm many middle-class families and imperil Democrats’ electoral hopes in 2016 and beyond. It’s only serious in that it’s a serious threat to the economy and to the priorities of the party that Sanders hopes to represent in the general election.

Contact Allen at jonallendc@gmail.com and follow him on Twitter @jonallendc.