The only thing that makes me think this might be a false flag is how close to the election this is.
None of these people are standing for office and even if the attacks were successful, it would have absolutely zero bearing on the election. (Except to make people aghast and possibly help the Democrats.) The timing is questionable.
HOWEVER, it's only a possibility, because the people who would mail a bomb to someone do not tend to be particularly rational. So, pointing out that the attacks are likely counter-productive is most definitely not a disqualifier for their source.