Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University.

(CNN) A common trope on the right is that the suspected bombs sent to Democratic Party leaders, CNN and critics of President Donald Trump couldn't have been sent by a right-wing terrorist.

On his radio show, Rush Limbaugh asserted , "Republicans just don't do this kind of thing."

Prominent conservative commentator Ann Coulter tweeted to her more than 2 million followers, "From the Haymarket riot to the Unibomber (sic) bombs are a liberal tactic."

Fox Business News anchor Lou Dobbs -- in a since-deleted tweet -- claimed that the devices were "Fake news-Fake bombs. Who could possibly benefit by so much fakery?"

Of course, we don't yet know the exact motivation of the person responsible for the mail bombs, but we do know that there is, in fact, a long history of political violence emanating from the far right. Claims that bombings are a liberal tactic, or that right-wing terrorists don't exist, are simply false.

Recall first that the 1995 Oklahoma City bombing was, at the time, the most lethal act of terrorism ever on US soil. The bombing killed 168 people and was carried out by Timothy McVeigh and Terry Nichols, who both had a long association with far-right causes.

Indeed, since 9/11, terrorists motivated by far-right ideologies have killed 73 people in the United States, according to New America, a research institution that tracks political violence.

Meanwhile, during the same time period in the United States, eight people were killed by terrorists motivated by black nationalist ideology, while jihadist terrorists have killed 104.

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Leftist terrorists have not killed anyone during this period in the United States, though an anti-Trump fanatic shot and gravely wounded Rep. Steve Scalise of Louisiana, senior House Republican, last year in Virginia when he was attending a baseball practice.

We simply don't know yet who is responsible for this series of pipe bomb packages or why they sent them, but those asserting that it couldn't be a right-wing terrorist clearly have no knowledge about the history of terrorism in the United States.