Right now there are two big progressive ideas out there: the Green New Deal on climate change and “Medicare for all” on health reform. Both would move U.S. policy significantly to the left. Each is sponsored by a self-proclaimed socialist: the Green New Deal by Alexandria Ocasio-Cortez and Medicare for all by Bernie Sanders. (Of course, neither of them is a socialist in the traditional sense.) Both ideas horrify not just conservatives but also many self-proclaimed centrists.

Yet while they may seem similar if you think of everything as left versus right, they’re very different on another dimension, which you might call purity versus pragmatism. And that difference is why I believe progressives should enthusiastically embrace the G.N.D. while being much more cautious about M4A.

You see, for all its sweeping ambition, the Green New Deal is arguably an exercise in pragmatism — in the proposition that the perfect is the enemy of the good.

What’s the perfect in this case? Climate-policy purists are focused on the notion of a carbon tax to discourage greenhouse gas emissions, and they look down on any proposal that doesn’t put such a tax front and center.