Not simply "exempt", unless you're referring specifically to the trade window part. There is in fact a law making it illegal to trade on insider information. https://en.wikipedia.org/wiki/STOCK_Act Arguably it did not go far enough.

I just don't think Congress has much in the way of insider information most of the time. Antitrust litigation would be one example where they do, but what else? Company insiders by contrast almost by definition have insider information.

One could make the case that the ability to influence the market itself is even more powerful than just knowing some inside data. And we are not even talking about things like defense contracts.

They should recuse themselves from any vote involving an industry that they have a more than trivial amount of stock in. Do you expect someone to restrict Big Tech when they have Facebook and Google stock?

Absolutely not, we are talking about politicians here. I like the idea of divesting into index funds during time in parliament / service.

If some Congressperson went short the market and then tanked the market though some statement that would indeed be very bad! Has anything like that ever happened? That would presumably nuke that person's reputation with costs far greater than whatever financial gains could be had.

If they're long the market and then boosting the market... I mean, isn't that what we want? You'd have to go further than a blind trust even and ban owning equities at all.

Of course they are. I guess that's one of the few cases on which all law makers can agree. Doesn't mean they should be exempt.