SLOWLY, THEN SUDDENLY: THE SAD STORY OF JOE BIDEN’S DECLINE.

“Gradually and then suddenly” is the story of Joe Biden’s physical and cognitive decline. “Gradually and then suddenly” is how his army of enablers in the media, the Democratic Party and the donor base abandoned his defense. “Gradually and then suddenly” is how he gifted his party and his country with a full-scale political crisis, centered on a president who no longer appears fit for office and whose vice president (and presumptive successor) is widely disliked.

Years ago, Ronald Reagan wrote, elegiacally, that the sun was setting on his life. But by then, he was a former president, living in retirement on his ranch. He was not occupying the Oval Office, holding down the most powerful and demanding job on earth.

Joe Biden is. The public no longer thinks he is fit to do that job. They reached that firm conclusion after watching the debate Thursday night and then hearing nothing from Biden’s allies to convince them otherwise. Whatever voters think of Biden’s performance for the last three-plus years, they simply don’t think he can continue. They are certain he won’t last another term and wonder if he will make it to the end of this one. They didn’t vote for the country to be governed by his staff.

That situation is a tragedy for Joe and his family and a source of anguish for his friends. He deserves our sympathy. But what doesn’t deserve sympathy is Joe’s decision, backed by his family and close associates, that he should stay in the race and remain on the job.

That decision affects all Americans. We depend on the president to lead the country and keep us safe in a dangerous world. That’s why Joe Biden’s decline goes far beyond a family tragedy. It’s a national tragedy and a palpable danger.

The debate made that danger conspicuous, unavoidable and indelible.

The “indelible” part is devastating politically. Most voters think, quite rightly, that the president is impaired, not temporarily but permanently. He may have good days and bad days, but he didn’t just have one bad night, as his defenders say. It was a bad night, certainly, but it was more than that. Joe Biden is visibly frail and forgetful, suffering long-term decline.

That impression has taken hold over the past few days and may already be set in concrete. If Joe cannot break it — a nearly impossible task — then he is doomed politically. Since he is currently atop the Democratic ticket, his fate will doom a lot of down-ballot contests as well.

And speaking of down-ballot, Joe is dooming those who chose to spend the last five years covering up for him: