Michael Beschloss's picks for 7 striking images of ex-presidents

With the five living presidents meeting Thursday in Texas, we asked presidential historian Michael Beschloss to give us a sense of these presidential gatherings. Beschloss, author of nine books and contributor to the PBS NewsHour and NBC News, had only to look at his Twitter feed, which features images such as this, from the opening of the George H.W. Bush library in 1997....