He has given up his “C.S.I.” reruns, consuming campaign coverage on Fox News — intently but fretfully — when he is perched in front of the television in his Houston home.

He reads three print newspapers daily, dials into briefings given by advisers to his son Jeb’s presidential campaign and stays up late to watch prime-time debates — after sitting through the so-called undercard, too.

Former President George Bush, 91 and frail, is straining to understand an election season that has, for his son and the Republican Party, lurched sharply and stunningly off script. And he is often bewildered by what he sees.

“I’m getting old,” he tells friends, appraising today’s politics, “at just the right time.”

These are confounding days for the Bush family and the network of advisers, donors and supporters who have helped sustain a political dynasty that began with the Senate victory by Prescott Bush, the older Mr. Bush’s father, in Connecticut 63 years ago. They have watched the rise of Donald J. Trump with alarm, and seen how Jeb Bush, the onetime Florida governor, has languished despite early advantages of political pedigree and campaign money.