During the late 1980s and early ’90s, when the country was at the exhausted end of a three-decade rise in violent crime, Biden was right there putting his fingerprints all over what would become America’s mass incarceration machine. He co-sponsored the Anti-Drug Abuse Act, which included much tougher penalties for crack cocaine than for powder cocaine, and lamented that “6 out of every 10 criminals who are arrested on drug charges have their cases dropped.”

Now that even a law-and-order Republican president is pushing through criminal justice reform, Uncle Joe is characterizing his role in the crack/powder disparity as a “big mistake.”

Biden absolutely will follow, not lead, on legalizing marijuana, which two out of three Americans — and all 12 presidential candidates immediately behind him in national polls — now support. Even while serving in the White House with “Choom Gang” emeritus Barack Obama, the then-veep was still using old-timey prohibitionist language, calling pot a “gateway drug.”

Think of every time American public opinion over the past half-century swung toward a public-policy hysteria many would eventually regret, and you’ll see Joe there, Zelig-like, flashing his choppers.