Mr. Biden’s speech contained 2,575 words, of which 1,363, or 53%, were general talk about uniting the country and so forth. Seven hundred fifty-four words, or 29%, were devoted to Covid. A mere 88 words—3% of his remarks—concerned his governing agenda of raising taxes on the wealthy, reforming health care to make it more “affordable” and “accessible,” passing “the Biden climate plan,” and addressing “systemic racism.”

Mr. Biden’s core message—that unity is essential to fixing America’s politics and restoring trust in its government—has been a powerful one throughout the country’s history. But it has been deployed most effectively by candidates with a vision for governing.

Ronald Reagan preached unity to turn the page on a period of malaise but backed it up with a fairly comprehensive agenda built around tax cuts, a stronger military and a smaller role for the federal government. Battling a depression, FDR rallied the country under the banner of “Happy Days Are Here Again,” but he used his closing address on Oct. 31, 1932, to repeat promises of unemployment relief, public works and temporary government jobs. William McKinley ended the Gilded Age’s angry politics with calls in 1896 for unity—reconciliation of North and South and a welcoming attitude toward immigrants. But he linked that with a prosperity agenda of sound money and protectionism.

With Mr. Biden, unity is based on only one thing: removing Mr. Trump from office.