Liz Warren this week echoed fellow Sen. Kamala Harris’ support for reparations payments to African-Americans on account of slavery. Count it as a sign of just how extreme and irrelevant are Democrats heading into the race for the 2020 nomination.

The reparations idea has gained new life in some circles thanks to radical writer Ta-Nehisi Coates, but it’s both wildly impractical and morally confused.

Yes, slavery was a grievous wrong, but no mere cash payment can make it right. Indeed, the whole effort is sure to increase America’s racial divisions, not end them. (Of course, Coates is deadly pessimistic about any hope for real racial peace.)

The problems are huge enough that both President Barack Obama and Sen. Bernie Sanders have nixed reparations as worth adopting. Pursue social justice and boost opportunities for underprivileged Americans, sure — but don’t go down this dead end.

Not that Harris or Warren seem to have anything specific in mind: They just didn’t dare slap the idea down when asked about it. Pressed for details, they gave boilerplate (Harris: “Change policies and structures . . . Make real investments in black communities”; Warren: “Confront the dark history of slavery and government-sanctioned discrimination”).

Neither candidate has bothered to think reparations through; they just know the word sounds good to some, and might somehow help win the White House.