I don't know about most political debates. I have read all of Lincoln's speeches and writings and that includes the famous Lincoln Douglas debates. Those were a series of 7 debates between Abraham Lincoln and Stephen Douglas where they were competing to become the next Senator from Illinois. Each candidate was given a total of 90 minutes to speak per debate. The debates were recorded and reported in detail in newspapers across the nation. Although Lincoln lost that election, the impression led him to being nominated to become President later on. The debates are amazing to read. The question was slavery and future of the nation was at stake. I highly encourage you to have a read of both sides of the debate. Even just chose one of the days rather than all 7. They are absolutely nothing like today's sound bites.

Followup question, as I've just been starting to browse through the, frankly, enormous debates that took place between Lincoln and Douglas (thank you /u/Steveweing ).

What have been the major milestones for debate format changing in American history?

I can only presume that major changes came about with the introduction of radio and subsequently television, but what else caused the format to change so drastically from Lincoln's time until today?

When the United States was founded politics functioned much differently than today. To the gentlemen of the eighteenth century, actively campaigning was seen as beneath them. Today we value candidates that are often outspoken and loud. Back then men distinguished themselves by their "self-governance." Washington exemplified this in spades. He was always in control, rarely let his emotions be seen in public, and, most importantly, attained power by refusing it. This seems completely contradictory, but to them ambition was a vice. Washington, by laying down his sword after the Revolutionary War proved to the nation that he was, beyond doubt, able to govern himself to an almost un-human level. Because of this, he gained much more respect than he would have if he acted as Napoleon did and led his army into the capital, which most people around the world expected.

So, active campaigning was seen as beneath the candidates. Washington, Adams, and Jefferson didn't stand on stumps and debate each other. They were public figures that allowed others to argue on their behalf. Political debates often occurred behind closed doors or in the newspapers, where members of a certain candidate's party would write compelling details about why their candidate was superior and often filthy slanders against the opponent. The candidates were active in politics, but allowed their reputations, both from their actions and their writings, to speak in place of their public voice. Of course, this all changed as the culture changed and candidates increasingly sought out the public's opinion, and this could only be garnered by directly engaging them.

If you're interested in changes in legislative debate practices, take a look at Robert Caro's Master of the Senate, the third volume in his biography of Lyndon Johnson. This is a subreddit favorite, and highlights Johnson's rise from junior senator to Majority Leader. Along the way, in true Caro fashion, it features lengthy and worthwhile digressions exploring important American institutions and historical figures.

Caro's great contribution to the issue of political debate is his 100-page, three-chapter "introduction" to the book (see this Google Books excerpt), which charts Senate history from the founding through the beginning of Johnson's tenure. Caro argues that the Senate was a "dam" designed to break waves of public opinion, and temper the passions of popular politics, a purpose it served admirably through America's early crises. In this, Caro is on extremely sound footing: Madison's Federalist 63 described that very quality as one of the Senate's virtues.

But by the time of the Depression, Caro continues, the Senate was a victim of its own success, and prevented the country from pivoting to meet new challenges. Johnson would change that, he concludes, by sacrificing classic virtues of statesmanship and gentlemanly debate in favor of brutal efficiency. In the final analysis, we are asked to contrast Calhoun's debates with Clay during the early 1800s, which shaped public opinion and changed minds, with Johnson's rapid-action, personality-driven legislative style ("call the vote!").

In Germany, beer halls were a common place to drink lots of lovely German lager, and also discuss recent events and politics.