Four former presidents were in attendance: her husband and her son, obviously, along with Obama and Bill Clinton. They were joined by Hillary Clinton, Laura Bush, Michelle Obama and Melania Trump in that stirring photograph, which went viral only partly because their easy smiles suggested a comity and dignity still possible in this hyperpartisan era. It also captured the country’s attention because of who was conspicuously missing — who wouldn’t have fit and didn’t belong. Comity, dignity and Trump cannot exist in the same frame.

Skipping that funeral wasn’t remarkable in the abstract. When Obama was president, he took a pass on both Betty Ford’s and Nancy Reagan’s; Michelle went in his stead. When George W. Bush was president, he didn’t attend Lady Bird Johnson’s — Laura did.

But Barbara Bush was a legendary figure in Trump’s own party. And neither President Obama nor President Bush would have had to worry about the foul memories and ill will stirred up by his presence.

Trump is a whole new, supersized kind of pariah: president non grata. He has made that many enemies, indulged in that much tactlessness and worked that diligently to consign apology and atonement to the dustbin of leadership.

Prince Harry and Meghan Markle are to be married in a week and a half, and decided not to invite major political figures, but imagine if they had wanted to. Obama would have been a logical inclusion, given that he and Harry have partnered in philanthropic work.

But Trump would have been unthinkable. In a past life, he repeatedly entertained questions from Howard Stern about whether he would have slept with Harry’s mother, Princess Diana. Yes, he said, although he once qualified that answer by saying that he would have insisted first that she take an H.I.V. test. It’s the gentlemanly thing.

Other presidents had their feuds. Other presidents rose above them. George H. W. Bush eventually became close friends with Bill Clinton, whose 1992 victory denied him a second term. Obama campaigned passionately against George W. Bush’s foreign debacle and fiscal recklessness, but there’s no vestige of that in the body language between Bush and Michelle Obama whenever they meet. It communicates a fondness that transcends politics. And it’s possible because each can see in the other many moments of generosity and genuine warmth.

In that image from Barbara Bush’s funeral, George W. is sandwiched between two other former first ladies — his wife, Laura, and Hillary Clinton — with an arm draped gently around each. Michelle and Melania are side by side, as if joined in a common mission. They are. It’s called decency.