It worked with Clinton. They have a bit less time to taint Comey, but I imagine the strategy is just about getting through the next couple of days until the next Trump tweet.
As far as combatting Gish-galloping fellow-travellers goes, pick a point, any point, you know is wrong and you know you can demolish. Stick with it even as the troll tries to avoid giving a straight answer and tries to go on to another point. Keep it up until you're confident that everyone can see the troll for what he is.
Otherwise, if you have the time and resources, start a wiki, let your compatriots have editing rights and no-one else, and write up an answer to each point when you have the time.
The thing about Gish-gallopers is that very few of them actually know what they're saying in any deep sense. While it can look formidable at first, like Trump's wall on closer examination a gallop can usually be found to have weak foundations and numerous gaps.