Joe Biden entered elective politics as a councilman in New Castle County, Del., in 1970, just this side of a half-century ago. Remember the Sony Walkman? Mr. Biden, now 76, was in politics for nearly a decade before it was introduced.

The Biden presidential campaign resembles one of those elegiac Western movies set around 1913, with weather-beaten men on horseback trying to pull off one last bank heist before getting run off the range by the arrival of motorcars on Main Street.

To accomplish this improbable feat, Mr. Biden is refashioning himself mainly as two things—the anti-Trump candidate and the second coming of Barack Obama.

The substance of Mr. Biden’s anti-Trump pitch strikes me as mysterious. The main argument for choosing him over the 20 or so Democrats running is that the “Scranton Scrapper” will win back the blue-collar voters in Pennsylvania, Michigan and Wisconsin who gave Donald Trump his margin of victory over Hillary Clinton.

But since last week’s announcement video, one of Mr. Biden’s signature lines has become that Donald Trump poses “a threat to this nation . . . unlike any I had ever seen in my lifetime.” How weird is it to insult your target audience by suggesting their Trump vote was an act of unprecedented stupidity?