Rep. Alexandria Ocasio-Cortez (D-N.Y.) on Capitol Hill last week. (Shawn Thew/EPA-EFE)
Opinion writer

President Trump promised a magnificent health-care system that cost less, gave more choices and provided better care. Such a plan never existed. In the less-than-exacting mainstream coverage of his campaign, he escaped scrutiny in a way Hillary Clinton or Sen. Bernie Sanders (I-Vt.) did not on their health-care proposals. That was a failure of the media but also a campaign lesson for candidates: If you are going to be specific about very, very ambitious proposals, you better be able to explain how you enact them.

We have seen this play out in the preliminary skirmishes in the Democratic presidential race on Medicare-for-all and on the Green New Deal. As to the latter, the GND (at least one version of it) is a resolution (i.e., a wish list), that declares it the “duty” of the federal government in 10 years to, among other things, achieve “net-zero greenhouse emissions," ensuring that any infrastructure bill considered by Congress address climate change and “meeting 100 percent of the power demand in the United States through clean, renewable and zero-emission energy sources." It also throws is a grab bag of “guarantees” for housing, union jobs and “justice and equity by stopping current, preventing future and repairing historic oppression of indigenous peoples, communities of color, migrant communities, deindustrialized communities, depopulated rural communities, the poor, low-income workers, women, the elderly, the unhoused, people with disabilities and youth.”

How we obtain, define, pay for and pass all of those things remains unexplained. Its sponsors want to avoid answering all the hard questions and simultaneously maintain the pretense that they have a concrete plan. Instead, they wind up being criticized for a plan that costs — dream up a big number, say, $5 trillion — and that can be obtained only through a command-and-control economy that most Americans abhor. Saying you support the GND, then, means what precisely?

One interpretation is that, sure, you’d insist we spend trillions and turn the economy inside out. You’d push for this or nothing even though such a plan is out of the realm of possibility. Well, if you don’t dream big, you don’t get it! If that’s the meaning behind “signing on to the GND,” then progressives are in for a heap of well-deserved criticism and the Democrats risk losing the opportunity to oust Trump. The voters are asked to choose between climate change denial and climate change fantasy.

Another interpretation of “sign on to the GND" is that you simply endorse the GND’s general goals. You’re giving thumbs up to what House Speaker Nancy Pelosi (D-Calif.) called the “Green New Dream — or whatever they call it.” That’s like saying you want to cure cancer by the end of the century. It’s not meant to be taken literally; it’s inspirational, like world peace.

The problem, however, is that once you say you “support the GND,” you are stuck defending the text of the GND. (And by the way, there is considerable confusion about what is actually in the GND. Anyone who signs on to something this far-reaching without nailing down specifics is going to get slammed.)

Turning very ambitious goals into precise mandates is fraught with political peril and altogether unnecessary. Take away the 10-year mandate and set out reasonable goals, for example, to “reduce greenhouse emissions by X percent.” Then you can lay out some concrete ways to get there (e.g., spend X on public transit, set fuel efficiency standards at Y, eliminate subsidies to fossil-fuel producers). That’s how legislating and governing actually work, and it is one way to allay fears that Democrats are wild-eyed radicals bent on wrecking the economy in the name of unattainable ends. The exercise winds up discrediting the altogether reasonable and urgent need to make progress to slow climate change.

It’s frankly dishonest to pledge to achieve nirvana in 10 years, falsely telling voters they can have the moon and the stars without much difficulty. It’s only one step removed from “I alone can fix it” and from the nonsensical claim that the solutions are easy and all agreed upon, just the will is missing.

In the Trump era, Democrats may be tempted to be as dishonest and irresponsible as Trump. That’s bad for our democracy and bad for Democrats, who must overcome the suspicion that they are irresponsible “socialists."

Here’s free advice for the Democratic field: Instead of signing on to pie-in-the-sky proposals, sign on to goals the vast majority of Americans want (health care for all!). Then show voters how we might get from here to there, or at least get closer to “there.” That means treating voters like adults and connecting campaign proposals to attainable legislative ends. That’s the way to earn voters’ trust. And it might be the difference between winning and four more years of Trump.

Read more:

Megan McArdle: ‘We’re nuts!’ isn’t a great pitch for a Green New Deal

David Von Drehle: Democrats refuse to be the only ones limited by reality

The Post’s View: President Trump, here’s ‘what the hell is going on’ with global warming

Eugene Robinson: A ‘Green New Deal’ sounds like pie in the sky. But we need it.

Tom Toles: Here’s the case against the Green New Deal, by analogy