Michael Beschloss — American Historian born on November 30, 1955,

Michael Richard Beschloss is an American historian. A specialist in the United States presidency, he is the author of nine books. In November 2013, he was appointed as a contributing columnist on history for The New York Times. His regular "HistorySource" column appears in the "Upshot" section of the newspaper. It is also published in the print Sunday New York Times... (wikipedia)

First of all, there's no mention of political parties in the Constitution, so you begin American history with not only no political conventions but also no parties.
The Founding Fathers would be sorry to see that America had become so divided and factionalized.
To people who remember JFK's assassination, JFK Jr. will probably always be that boy saluting his father's coffin.
So the result was that as one approached a political convention for most of the 19th century and for most of the 20th century until the 1960's, part of the drama was the fact that you didn't know ultimately who was going to be the nominee at the end of that convention week.
The founders were very worried that if parties developed in America, you might have something like the modern Italian system, where you have 20 different parties that divide Congress and the country and can't govern.