Ruth Ben-Ghiat is a frequent contributor to CNN Opinion and a professor of history and Italian studies at New York University who writes about authoritarianism and propaganda. Follow her @ruthbenghiat. The opinions expressed in this commentary are solely those of the author. Read more opinion articles on CNN.

(CNN) Anyone who wonders about the link between hateful threats and actual violence was given something serious and grave to think about this week. Authorities found several pipe bombs delivered to people and organizations that for years have been on the receiving end of a flood of right-wing hate speech.

First it was billionaire philanthropist George Soros: A pipe bomb was found on Monday in his mailbox in Westchester County, New York. On Wednesday, bombs were mailed to Hillary Clinton, Barack Obama, former attorney general Eric Holder, and CNN's offices in Manhattan. The CNN bomb was addressed to Obama administration CIA Director John Brennan. (Only the one directed at Soros, who as a private citizen does not have Secret Service protection, arrived at its destination; the others were intercepted by law enforcement).

We don't know who did this, though authorities suspect all the devices were made by the same person or group. It's a sad commentary on our times that the motivations could be multiple. Sowing or threatening violence in many places over a short space of time is a classic tactic of terrorists, and others who wish to destabilize society -- for example, ahead of an important political event.

The midterm elections, coming up in less than two weeks, fit this bill. Republican Party efforts at voter suppression have made for a tense climate that President Donald Trump has worsened by insinuating that Democrats, whom he calls an "angry, leftist mob," may commit voter fraud.

The charge recalls the starring role of hate speech -- and repeated allusions to violence -- that have characterized Trump as a candidate and President. Who can forget Trump, in 2016, pretending to pull a trigger as he "joked" about "Second Amendment people" acting against Clinton, or elected Republican officials like Oklahoma State Rep. John Bennett and New Hampshire state Rep. Al Baldasaro calling for her execution?