Story highlights George Ciccariello-Maher says the threats began a year ago

His situation has raised questions about free speech on campuses

(CNN) A Drexel University professor who received death threats after posting several controversial tweets said Thursday he is resigning because the year-long harassment has made his situation "unsustainable."

George Ciccariello-Maher, a professor of politics and global studies, had been teaching his class remotely via video conference after being put on administrative leave, a move that Drexel said was for his own safety.

The professor said his resignation is effective December 31.

"This is not a decision I take lightly; however, after nearly a year of harassment by right-wing, white supremacist media outlets and Internet mobs, after death threats and threats of violence directed against me and my family, my situation has become unsustainable," Ciccariello-Maher wrote on his Facebook account. "Staying at Drexel in the eye of this storm has become detrimental to my own writing, speaking, and organizing."

After December 31st, 2017, I will no longer work at Drexel University. pic.twitter.com/bAM37dbv1q — George Ciccariello (@ciccmaher) December 28, 2017

The professor said the threats began last December after he posted on Twitter: "All I Want for Christmas is White Genocide." He said the tweet was a joke, a "satirical jab at a certain paranoid racist fantasy and that white genocide does not exist."

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