Drexel University professor George Ciccariello-Maher was forced to resign after a year of death threats made his position at the university “unsustainable,” according to a statement that he released this week.

Ciccariello-Maher, a professor of politics and global studies, was harassed after several tweets he made were criticized on various right-wing outlets. Throughout the ordeal, Drexel University has criticized the professor and refused to support him.

The threats began last year in December, when Ciccariello-Maher tweeted that all he wanted for Christmas was “white genocide.” The tweet went viral, with many right-wing websites calling for Ciccariello-Maher to be fired. Drexel University condemned the tweet, calling it “utterly reprehensible” and “deeply disturbing,” and arranging a meeting with Ciccariello-Maher to discuss the matter.

Cicariello-Maher stated that the Tweet was satirical, intended at mocking the concept of “white genocide.” He said at the time that it was a “satirical jab at a certain paranoid racist fantasy,” and that white genocide is an “imaginary concept” to marshal support for right-wing forces.

In April, the professor made headlines again after tweeting his reaction to a first-class passenger giving up his seat to a soldier. “Some guy in first class gave up his seat for a uniformed soldier. People are thanking him. I'm trying not to vomit or yell about Mosul,” he wrote.

The comment came two days after a US airstrike in Mosul, Iraq killed 200 civilians, one of the deadliest massacres of civilians in Iraq.

Cicariello-Maher said his Tweet was intended to question the way many Americans support the military without demanding accountability, or that the United States provide sufficient health care and support for veterans and active-duty members.

Drexel University placed Cicariello-Maher on administrative leave in October, forcing him to teach his classes online or via Skype, after he tweeted the Las Vegas shooting was the result of “Trumpism” and the “narrative of white victimization.”

The university said that it was suspending Ciccariello-Maher not because of his views, but for safety, given the threats he was receiving. However, it was clearly a maneuver to accommodate the right-wing campaign.

In an interview with CNN, Ciccariello-Maher said he received over 800 voicemails with some even threatening his son. In a Facebook statement, he said his resignation “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.”

The attack on Ciccariello-Maher is part of a broader phenomenon. The American Association of University Professors (AAUP) said more than 100 incidents of targeted harassment against professors have been reported on college campuses in the past year. The AAUP came to Cicariello-Maher’s defense, stating that Drexel University bowed to the pressure of those threatening him.

In the past year, conflicts over free speech on college campuses have escalated. Right-wing websites such as campusreform.org have drawn attention to professors they allege “discriminate against conservative students and advance leftist propaganda in the classroom.” They have been encouraged by the election of Trump, with Democrats doing nothing to mobilize opposition.

Last December, death threats forced an Orange Coast College professor to leave California after a video surfaced of her telling her students that President Trump’s election was an “act of terrorism.” In June, an Assistant Professor at the University of Iowa was bombarded with hate mail after one of her lectures claimed that the exaltation of white marble statues fueled white supremacy.

At Evergreen State College, professor Bret Weinstein became the target of a racialist campaign from pseudo-left groups after speaking out against a college-sponsored event that called for all white students to leave campus grounds for a day. Weinstein was portrayed as a supporting white supremacy for stating that asking for white students to leave the campus “is a show of force and an act of oppression in and of itself.”