Vice President Kamala Harris didn’t just call special counsel Robert K. Hur’s report “gratuitous, inaccurate and inappropriate” when it came out in February. She claimed he was “clearly politically motivated” and impugned his integrity.

Mr. Hur, appointed by Attorney General Merrick Garland to investigate President Joe Biden’s mishandling of classified material, recommended that the 81-year-old not face charges, partly because a jury could reasonably conclude that he’s “a sympathetic, well-meaning, elderly man with a poor memory.”

That assessment was based on Mr. Biden’s frequent forgetfulness and hazy answers during five hours of interviews with prosecutors.

Mr. Hur has been repeatedly vindicated during the intervening nine months. The interview transcripts, when they came out, bolstered his conclusions. If anything, the truth was worse than what Mr. Hur described.

It’s now acknowledged almost universally that Mr. Biden should not have sought a second term, but the Democratic establishment denied the obvious and propped him up politically, even as evidence of his decline mounted.

Prominent Democratic politicians changed their tune only after a disastrous debate performance in June made it impossible to conceal Mr. Biden’s frailty from the public any longer — and forced them to confront the possibility of electoral disaster in November.

The credibility problems that Ms. Harris’s repeated defense of Mr. Biden’s sharpness illustrated were part of the reason Democrats met defeat.

Make no mistake: As dissemblers go, President-elect Donald Trump has no equal, and his dishonesty is a continual disgrace. Even his strongest supporters acknowledge he exaggerates for effect and plays fast and loose with facts. But voters obviously see other qualities in him that offset his dishonesty, perhaps drawn from rosy recollections of living under the first Trump presidency.

Democrats tried to make fidelity to science, facts and truth their distinguishing characteristic as a party. The White House’s aggressive coverup of Mr. Biden’s decline undermined that claim. Rep. Dean Phillips (D-Minnesota) was the only lawmaker willing to challenge Mr. Biden for the Democratic presidential nomination.

He was ostracized and lost his spot in House leadership. Mr. Biden’s allies concocted terms such as “cheap fakes” to dismiss embarrassing video clips in which Mr. Biden appeared dazed, confused, tired and inaudible. Allies of the president frequently labeled content they didn’t approve of as ” disinformation,” cheapening the term.

The harder they spun, the less believable they became. White House press secretary Karine Jean-Pierre said days after the June 27 debate that Mr. Biden was ” as sharp as ever.” Eventually, Mr. Biden bowed to reality and stepped aside.

But Ms. Harris struggled whenever she was asked to explain her defenses of Mr. Biden. On Oct. 22, NBC’s Hallie Jackson pressed Ms. Harris five times on this topic. The vice president dodged when asked whether she ever saw anything like what happened during the debate behind closed doors. “It’s a judgment question, that’s why I ask,” Ms. Jackson responded. “Can the American people trust you in these moments, even when it’s maybe uncomfortable?” Ms. Harris did not answer directly.

To the bitter end, Mr. Biden’s team has covered for him. In the last week of the campaign, White House press staff altered the official transcript of a public appearance in which Mr. Biden described Trump supporters as “garbage.”

The Associated Press reported that an apostrophe was added to the initial version prepared by the official White House stenographers so it would appear that he was referring only to a single supporter: the comedian who had joked that Puerto Rico is a ” floating island of garbage.”

All of this took a toll on believability. Polls showed more voters believed that Mr. Trump would actually implement his campaign promises than Ms. Harris would hers.

The record does highlight one of the things Democrats must do to resuscitate their brand: live up to their billing as truth-tellers.