Good lord, President Biden’s decline is painful to watch: On Wednesday, he humiliated himself multiple times over the course of a paint-by-numbers speech.

He dropped into Pueblo, Colo., to tout what the White House says is the world’s largest wind-tower factory, aiming to take credit for creating “good, green jobs” and so bolster his subterranean polls on the economy.

But he couldn’t stop himself from ad-libbing disastrously.

He opened with a failed joke about the nuclear “football” — introducing himself to worker by announcing, “Now look, my Marine carries that, but it has the code to blow up the world,” before pointing to the machinery and mock-asking, “This is not nuclear weapons, is it?”

He followed with some “senior moment” borderline-racism: Addressing the South Korean corporate plant owners, he bragged, “I am friends with your leader, Mr. Moon, you know” — plainly meaning Moon Jae-in, who exited as South Korea’s prez last year.

And Biden has since honored the current president of that land, Yoon Suk Yeol, at a White House state dinner in April, among other meetings at summits and so on.

Other lowlights included a reference to “Congressman Trump” and referring to Deng Xiaoping (who died in 1997) “in the Himalayas” in a story he’s previously told as featuring Xi Jinping, China’s current prez.

Biden’s staff already keeps him out of the public eye as much as possible, but at this rate he’s going to have to run for re-election without making any campaign stops at all: He was terrible months ago, and will only get worse.

Already, polls show that most Democrats want another candidate, but the party establishment won’t budge.

And any voter doubting he can possibly make it through a second term will take a quick look at (or, worse, hear) Kamala Harris and figure out if they can go Republican, third-party or move to another country.

Democrats, wake up: You’re doing neither the nation nor your party any good by sticking with this man, and it’s cruel to him.

Thank him for his service and find a candidate who can pass an elementary sniff-test.