I believe we need to make a clear distinction between “death threats” and “threats of violence”, versus acts of violence.
There are plenty of examples of both threats of violence, and of acts against property that suggest threats of violence. Three people were arrested last year for threatening congresspeople.
But there are very rarely any actual attacks. Threats are serious and should be dealt with, but our political rhetoric lends itself to threats that are just part of the discussion; our system lets people get things out of their system without resorting to violence.
BTW, Jim Geraghty over at National Review has found some recent uses of the term “blood libel” which support the idea that it is in more common usage. And better still, they include uses from the left.