Fresh from being named to a chair of outreach leadership position in the Senate, Vermont Senator Bernie Sanders called on Donald Trump to rescind Stephen Bannon’s post as chief strategist during a speech on Wednesday.

Speaking from George Washington University, Sanders doubled down on his view on Bannon, whose controversial new post in Trump’s administration has been met with widespread criticism. Bannon, the former head of Breitbart News, has given voice to racist, sexist, anti-Semitic and white nationalist views through Breitbart.

“The president of the United States should not have a racist at his side,” Sanders told the crowd. “I call up on Mr. Trump to rescind the appointment of Mr. Bannon.”

Earlier on Wednesday, Sanders called Bannon’s appointment “totally unacceptable,” in a statement.

The senator also took Trump to task over issues such as climate change, and said if Trump did not make an effort to move away from using fossil fuel, the planet would become far less “healthy and habitable” for future generations.

“Tell Mr. Trump to read a little bit about science,” he said.