False flag attack by some dipstuff antifa type is more likely than a right wing terrorist plot.
The timing so close to midterms is too convenient, for one. This would just energize the democratic base.
Someone smart enough to make the bombs also wired them in such a way that they would not detonate at all.
Whoever sent these had no intention of harming anyone. This is just a scare tactic and people are already smelling the rat stuff