While I believe in the feasibility, and -- god help us -- probability that such a "gas" exists, I don't believe there is evidence that it is used
in this manner. Those who stand against certain agendas, in the political world, are targets of an unaccountable, well oiled propaganda machine (Fox
news, for example), which is perfectly capable of ruining a persons reputation without the use of such weapons.
There is, of course, also the possibility that some of these people are indeed crazy

. You probably wouldn't realize it until you've spent time
around the person. How can you spend time around somebody you've only read about in the media? You can't, but you can listen to what they have to
say. The extent of how "bonkers," they are, becomes apparent over time.
The only problem with your hypothesis is that there is no "control." How can you tell the person, supposedly targeted by a gas attack, was sane to
begin with? How can you objectively measure how bonkers they are BEFORE and AFTER they seem to have changed?
I'd bet that most of the people you think have changed, actually haven't, and that the reason you think they have is because your initial impression
of them was formed by brief, non-revealing encounters through media, writings, or even real-life introductions. What you don't see is a history of
this persons past, which could reveal a pattern of mania, only obvious when you step back to look at the bigger picture.