Democrats are at a loss to explain vouching for President Biden’s mental faculties prior to his decline being laid bare. With books detailing the “cover-up” hitting shelves, the party keeps repeating stock denials rather than leaning into a simple fact: Love is blind. 

The 1966 hit “When a Man Loves a Woman” describes how the heart obscures judgment. “If she is bad,” Percy Sledge sings of the unnamed woman, a man “can’t see it. She can do no wrong.” It was the same for Democrats who fell for Mr. Biden.

On the “Talk Easy” podcast released Sunday, Sam Fragoso asks Senator Warren of Massachusetts if she regrets “saying that President Biden had a mental acuity” and “a ‘sharpness’ to him.” The senator says that she “had not seen decline.”

Mr. Fragoso asks again. Ms. Warren hasn’t seen “any decline” between 2021 and 2024? After a long pause, the senator says that Mr. Biden was “sharp,” “on his feet,” and she’d had “readings with him.” Standing and “can speak in sentences” was “not praise,” the host noted.

“Fair enough,” Ms. Warren says. Those moments she describes with Mr. Biden provided her an opportunity for confirmation bias, to see him as he had been rather than as he was. The human brain is a magnificent excuse factory.

Democrats entertained a similar pipe dream in 1904. Hoping to beat President Theodore Roosevelt, some put forth President Cleveland for a third, non-consecutive term. Although 12 years out of office, he was the only Democrat to win the White House since 1856.

Another denial of the toll exacted by time occurred in November. Those stuck in the 1980s glory days of the champion boxer, Mike Tyson, believed he would knock out Jake Paul, 31 years his junior. Instead, “Iron Mike” showed rust and lost by unanimous decision.

Expect questions about Mr. Biden to proliferate next month when “Original Sin: President Biden’s Decline, Its Cover-Up, and His Disastrous Choice to Run Again” is released. It’s a postmortem by the CNN anchor Jacob Tapper and Axios correspondent Alex Thompson.

Accounts like those in “Original Sin” and responses like Ms. Warren’s leave voters feeling that Democrats view them as dupes. The strongest part of the senator’s answer — “I said what I believed to be true” — is obscured by denials that seem implausible and go unexplained.

More effective spin came courtesy of a documentarian, Chris Whipple, who published this month “Uncharted,” on the 2024 campaign. “I differ,” he tolls NPR, with those alleging “a cover-up,” which “suggests that you’re hiding something that you know to be true.”

Mr. Whipple says that Mr. Biden’s limitations were lost in a “fog of delusion and denial.” An exchange that illuminates why the conditions were right for that fog to spread occurs in the Scopes Monkey Trial dramatization, “Inherit the Wind.”

Matt Brady — an elderly character based on the three-time Democratic presidential nominee, Secretary of State William Jennings Bryan — loses his fight against teaching evolution in schools. Upon learning of his death, a reporter mocks the defeated man for his failings. 

The defense attorney, Henry Drummond, defends his opposing counsel. “A giant,” he reminds the newsman, “once lived in that body.” Although Mr. Biden was the butt of bipartisan jokes as a senator and vice president, in the White House, Democrats came to view him as a giant, too. 

Americans might understand if affection for Mr. Biden blinded Democrats to his infirmities. They’re prone to sympathize with emotional pitches about age, as they do with anyone who puts off confronting an elderly parent about giving up their car keys.

Citing familiar scenarios where hearts overrule minds will enable Democrats to frame their defense of Mr. Biden in a better light. They misled themselves, too, they can say. Love makes fools of us all, and the party paid a steep price with Mr. Trump’s victory.

Until Democrats find an answer, they’ll be dogged by allegations of a cover-up. Their best strategy is to explain that emotions fogged their view of reality. And instead of seeing an enfeebled president when they looked at Mr. Biden, they saw a political giant who had one more knockout punch left.