How to counter a Gish Gallop during a live debate.

I've had to do this quite a few times, and there are several techniques that every experienced debater typically learns early on.

First, patiently listen and take notes until the person's time has run out, or they've run out of steam and start repeating themselves.

Pick out two or three of the points, preface it by saying something that indicates what the person did. You can explicitly name the Gish Gallop, but a lot of your audience won't know what that is. So you could use a phrase like, "That was a big nothing burger," or "Boy, he's trying to blow you up with a lot of hot air," or "That's an avalanche of nonsense and lies that I doubt anyone in the audience was fooled by."

Then you pick one of his weakest points, and say, "My opponent wants you to believe..." and then you deconstruct the point. You pick one of the most nonsensical claims, and you repeat it word for word, but in a context that heightens its nonsensicalness. And you say stuff like, "And does anybody know what he means by this? That sounds like a bunch of gobbledygook to me." This is all assuming that your audience is dumb enough to take the other guy seriously.

In a higher level debate, you actually go ahead and say, "You named a lot of things there. It seems like you didn't want to actually discuss anything; you just wanted to make a list. Pick your strongest point and let's discuss it."

Of course, none of this works if your brain is not working. Being able to think is a prerequisite to being able to debate. If you can't think, what you do is your best ignoring what the other person has said, and go down your own list of rhetoric. Of course, that doesn't work if you have trouble both thinking and speaking.

Of course, if you have trouble thinking and speaking, you really shouldn't be debating or have any sort of position of responsibility. Especially if you can't beat a fool that does a good job of embarrassing himself.