It is difficult to imagine Mr. Clinton, Mr. Bush or Mr. Obama rejecting a call for help from Mr. Trump, but it is equally difficult to imagine him calling. When asked at one of his early coronavirus press briefings whether he would reach out to his predecessors for help, Mr. Trump said dismissively: “I don’t think I’m going to learn much. And, you know, I guess you could say that there’s probably a natural inclination not to call.”

If Mr. Obama, Mr. Bush, Mr. Clinton and Mr. Carter were to start an effort together without Mr. Trump, a former Obama aide lamented, the endeavor would be entirely eclipsed by the fact that they did it without the sitting president.

Mr. Trump has clearly enjoyed humiliating his predecessors and has called Mr. Bush’s invasion of Iraq “the single worst decision ever made.” In a mid-March tweet, just as the nation’s economy was shutting down and schools were closing, Mr. Trump wasted no time criticizing his predecessor’s management of a previous health crisis. He railed against Mr. Obama’s response to the H1N1 swine flu and called it “a full-scale disaster, with thousands dying, and nothing meaningful done to fix the testing problem, until now.”

Mr. Bush recently wrote a note to his staff that was obtained by The Dallas Morning News. He expressed “absolute confidence in the experts who are in charge” of the nation’s coronavirus response. He said that he was “reading, painting and riding mountain bikes” and that he and his wife, the former first lady Laura Bush, were “handwashing and social-distancing to the max.”

But wouldn’t it be better if he and the other ex-presidents could put the lessons they learned in office to lift the country’s spirit during this public health crisis?

Of course each still has unique influence: Bill and Hillary Clinton sent hundreds of pizzas to hospital staff caring for coronavirus patients, and Jimmy Carter asked donors to “forgo” their “next gift” to the Carter Center and instead support groups working directly to combat the pandemic.

Mr. Trump has ended up with an opponent who is so much more in the mold of the presidential fraternity. Mr. Biden would not hesitate to call a predecessor or a former political rival during a crisis. Mr. Biden’s dozens of years in the Senate and two terms as vice president included many friendships with Republicans, and at least one with a former member of Mr. Trump’s cabinet.