You’re probably right although in my mind the Kennedy/Nixon debates did help Kennedy win the election. You may know better.
I think it's fair to concede that as a contributing factor, but where I would divert is that that particular year of debates was completely different from what we have now. They weren't "really" aware precisely how television could change the thing because they were learning.
But by 1992, every single debate was a scripted campaign speech. It was already getting that way some in 1988, but it got really bad that year - and then it went full on insane in the 96 GOP debates.
So I wouldn't dispute your assessment because JFK didn't. He was clear that he would have lost without the debates. However, JFK did not in any way clean Nixon's clock, either. He "won" because he looked calmer and more self-assured.
I watched a few 1988 Democratic primary debates - and BY FAR the best debater and candidate was Jesse Jackson. He had the wittiest lines, he came across as the least programmed candidate, and he looked Presidential (yes, he did).
He also didn't have a snowball's chance in hell of winning.
The "defining moment" (if you will) in the 2016 GOP race was when Chris Christie cut Marco Rubio to shreds on his claim of a "reading from a script." The funny thing is that to a large degree they all do that in these debates, but what Rubio SHOULD have done was something like this:
"Governor, I'm being consistent with what I say, which means I use the same words to communicate. I'm being consistent; a script is what Mr Trump reads from as a reality TV star. A script is what he gave you to make that point. And a script is what your appointees were following when they closed the George Washington Bridge. But as I'm open to taking advice, I will endeavor to expand my vocabulary a bit while remaining consistent."
His failure wasn't the reading from the script, it was how he handled it.
I’ve already made my mind up to vote for whoever stands the best chance of beating Trump so these Democratic debates will help me decide who to support. For example, I suspect if Sanders or Warren we’re to be nominated taxes would be dramatically raised, thus raising payroll taxes and possibly driving me out of business.
There was nothing to hold over Trump’s head in the 2016 election. He was not a Washington politician. Now he is.
The flip side to that is that no matter how much or little credit he deserves for it, we are at peace and the economy is humming along. And those two issues are what most folks vote, which is why though I concur with jthomas's observation of the perfect storm, the tendency to re-fight the last war is not going to help the Democrats (I think that's a lot of the problem with both Bernie and Biden).
Hopefully a good debater like Harris or Buttigieg can hold Donald Trump’s feet to the fire. Harris being a former prosecutor should be well equipped for the task. Whether or not it makes a difference in the election, I want to see that happen. Of course, I don’t know if I can afford Harris either, but I’m 100% certain Trump has to go.
Look, I'll even be one to grant there would be a certain poetic/karmic justice in Trump losing to a minority female candidate. But keeping your support is as simple as following G W Bush's way of debating: get back to the 3 points you want to make. (Bill Clinton was a master at this, but he had the intellect to sound like he was saying something more expansive than he actually was).
Just remember - 2011 and 2012 Alabama was about as close to an unbeatable machine as you're gonna see - and they lost two games. Trump isn't God, so he's not unbeatable.