Remember Hanlon's Razor, never attribute to malice that which is adequately explained by stupidity.
Conversely, we know some people are not stupid. I dislike marco Rubio's politics for example, but he's a smart guy and widely considered to be competent. And as an attorney and a US Senator of long experience in intelligence matters, there's no way he's unaware of the legal implications of using a self-destructing messaging channel.