Well ... radio is of course older than television, but prior to the outset of televised debates with Kennedy-Nixon in 1960, there were but three primary debates on radio, Stevenson-Kefauver in 1956, Stassen-Dewey in 1948, and a radio broadcast of Democratic and Republican hopefuls answering two questions each at a League of Women Voters Convention. FDR, a master of radio with his fireside chats, ignored Wilkie's challenge to radio debate in 1940. (See CNN's Presidential Debates in the Broadcast Era before 1960.)
The Kennedy-Nixon debates were broadcast on both television and radio. Those who saw the saw debates on TV thought JFK won; those who heard the debates on radio though Nixon was the victor. Many more people saw the debates on television, Kennedy won by a narrow margin, and television assumed the role as the preeminent political broadcast medium. (See my book, The Soft Edge: A Natural History and Future of the Information Revolution, for more on the turning-point significance of that 1960 debate.)
But radio still has its charms and value. I've been able to listen to this debate, without missing a word, while working on the computer, and grabbing a bite to eat - it's liberating not being glued to the screen. My wife just got home - she was listening to the debate in the car (hey, we're not only a tv-watching but a political family). Radio, like all acoustic media, is much amenable than visual media to multi-tasking.
The pace also feels more contemplative and leisurely - at this point, a little over an hour into the debate, only one of three main topics has been addressed - Iran. Next up will be other foreign policy. I of course already knew the positions of all the contenders prior to the debate, but it seemed to be me that points of view came through a little more clearly on radio than television.
I just heard that the Republicans were invited to do a radio debate ... but somehow couldn't work out the logistics. Late on YouTube, opting out of radio - there apparently is not an abundance of media savvy in most of the Republican campaigns. (I do know this for a fact - but I bet that Mike Huckabee and Ron Paul would have been happy to do a radio debate.)
Back to the debate. I'll be sipping a nice cup of tea...