There do seem to be a lot of these ricin attacks, at least when you extend the timeframe. Sometimes years go by between attacks but they keep coming. It makes you wonder if the FBI is ever bothering to investigate.
The timing of the ricin attacks so far seems to involve domestic politic tensions of the left-wing variety. Putting Cruz in the hospital, or even just giving him a good scare, might be the one vote the left needs to stop Kavanaugh.. and why not go after the one Senator you hate the most, in that case?
When you dehumanize your political opponents and characterize their ideas as violence, some people are going to behave violently. I'm more and more convinced this isn't just considered acceptable to the left. More and more it seems to be the intended result.