Democratic voters clearly aren’t buying the “electability” argument against Bernie Sanders, and they may be right. But the real question is: Are his rivals willing to make a serious policy case against him?

We don’t think James Carville is wrong to pooh-pooh the theory that Sanders will “galvanize heretofore sleepy parts of [the] electorate” to win in November, but President Trump’s victory in 2016 is ample proof that the old rules about ideological appeals miss how American voters think these days.

Which leaves it to the Democrats trying to derail Bernie to finally flag the utter lunacy of his policies.

It’s not just that Medicare for All would be insanely expensive, or even that it would force half the country to give up the private health insurance they have now: It’s that it would inevitably lead to rationing of care, because governments are horrible at investing wisely in everything from R&D to basic infrastructure. (Look at your roads, New York!)

And the Green New Deal — which all the candidates embrace for fear of losing to Bernie and the left — is arrant nonsense: a huge pile of outdated socialism on top of “anti-carbon” moves that would devastate the US economy.

Not to mention the foreign policy of a guy who keeps looking at the bright side of anti-democratic socialism, from the old USSR to Castro’s Cuba to Venezuela today.

As if Fidel Castro’s “massive literacy program” made up for the way he turned Cuba into one of the hemisphere’s poorest nations, yet kept power because (as Sen. Marco Rubio put it) “his opponents were jailed, murdered or exiled.”

If they don’t find the guts to start calling out Sanders’ extremism now, his Democratic rivals will be toast by the end of Super Tuesday.