What happened? Surely part of it is culture. While we live in an age of Twitter-fed self-promotion and self-assertion, Mr. Bush believes in reticence and in dignity. Bill Clinton and Ross Perot mastered cable TV; Mr. Bush might well have thought Arsenio Hall was a building at Andover. Talk radio was on the rise in the late 1980s and early ’90s, as was reflexive partisanship. Rush Limbaugh, who endorsed Pat Buchanan’s primary challenge against Mr. Bush in 1992, embodied the former; Newt Gingrich, who broke with Mr. Bush over the 1990 budget agreement, was the leading example of the latter.

Mr. Bush, who began his political career in Texas fighting the John Birch Society, has never been truly at home in what’s become the Breitbart universe. In the aftermath of the loss of his first race for office, in 1964, Mr. Bush wrote a heartfelt letter to an old friend: “This mean humorless philosophy which says everybody should agree on absolutely everything is not good.” He continued, “When the word moderation becomes a dirty word we have some soul searching to do.”

The words — touchingly naïve and heartfelt — seem to come from a vanished world. The product of Greenwich Country Day School, Andover and Yale, Mr. Bush was the last president of the World War II generation. A decorated combat hero, he nevertheless found it incredibly difficult to talk about himself — a legacy from his mother, who discouraged self-reference and self-absorption by saying that no one wanted to hear about the Great I Am. As a child, Mr. Bush was nicknamed Have-Half for his tendency to split any treats in two to share with friends. His was an ethos of empathy. Mr. Bush always wondered about what “the other guy” was thinking and feeling. That was Mr. Bush’s reality — one far removed from Mr. Trump’s Hegelian assertions of his own power, prowess and centrality.

As temperamentally distinctive as Mr. Bush is from Mr. Trump, historians seeking to tell the story of the devolution of the Republican Party will also find that the forces that gave us 2016 have roots in the first Bush administration. Mr. Atwater and Roger Ailes, who worked for the Bush campaign in 1988, practiced a rough politics of conservative populism. A pragmatist when it came to amassing power, Mr. Bush was willing to do what it took to defeat Gov. Michael S. Dukakis of Massachusetts, running a campaign that painted Mr. Dukakis as soft on crime for his record of furloughing convicted murderers and criticized his veto of a bill mandating that public schoolchildren recite the Pledge of Allegiance.

The difference between 1988 and 2016, however, is that for Mr. Bush such attacks were the means to an end: a victory that would enable him to focus on what he truly cared about, which was governance. For Mr. Trump, the means are the end — he is, as Jeb Bush aptly put it during the 2016 primaries, the chaos candidate. The elder Bush used to dismiss campaign posturing with a phrase of Mao’s, calling such blasts “empty cannons of rhetoric.” Mr. Trump can’t get enough of such cannon fire.