STANFORD (CBS SF) – Dr. Scott Atlas, a fellow at Stanford University’s Hoover Institution who has faced controversy for advising President Donald Trump on the COVID-19 pandemic, has resigned.

CBS News confirmed with the White House on Monday that Atlas has resigned after nearly four months with the administration, but officials would not give a reason why. In his resignation letter, Atlas thanked Trump for “the honor and privilege to serve on behalf of the American people.”

“I worked hard with a singular focus—to save lives and help Americans through this pandemic,” Atlas went on to say.

The doctor also appeared to express well wishes for President-elect Joe Biden and the incoming administration, at a time where Trump has repeatedly spread baseless claims of election fraud and has refused to concede nearly a month after Election Day.

“I sincerely wish the new team all the best as they guide the nation through these trying, polarized times,” Atlas said. “With the emerging treatments and vaccines, I remain highly optimistic that America will thrive once again and overcome the adversity of the pandemic and all that it has entailed.”

Since joining the Trump administration in August, Atlas faced controversy for clashing with members of the White House Coronavirus Task Force, along with numerous statements downplaying the use of masks and criticizing lockdowns to slow the spread of the coronavirus.

The doctor was also condemned over a tweet where he urged the people of Michigan to “rise up” against Gov. Gretchen Whitmer after she enacted public health measures in response to rising COVID-19 cases. Atlas later clarified his remarks, saying he was not trying to encourage more violence against Whitmer and was talking about voting and peaceful protest.

Earlier this month, Stanford University faculty approved a measure condemning Atlas, calling his behavior “anathema to our community, our values and our belief that we should use knowledge for good.”

“What Atlas has done is an embarrassment to the university,” Dr. David Spiegel of the Stanford School of Medicine said at the time.

The university’s measure stopped short of asking university leaders to investigate Atlas for possible sanctions, amid concerns about academic freedom.

According to Fox News, Atlas’ role as a temporary Special Government Employee (SGE), was set to expire this week.