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Dr. Eric Lander, a former member of President Biden's Cabinet who served as director of the White House Office of Science and Technology Policy (OSTP), resigned Monday evening after an internal White House investigation found credible evidence he had spoken harshly and disrespectfully to colleagues in front of other colleagues.

"I am devastated that I caused hurt to past and present colleagues by the way in which I have spoken to them," Lander wrote in his letter of resignation. "But it is clear that things I said, and the way I said them, crossed the line at times into being disrespectful and demeaning, to both men and women. That was never my intention. Nonetheless, it is my fault and my responsibility. I will take this lesson forward. I believe it is not possible to continue effectively in my role, and the work of this office is far too important to be hindered."

Eric Lander

Eric Lander speaks to members of the media after being sworn in by Vice President Kamala Harris in the Eisenhower Executive Office Building in Washington, D.C., on June 2, 2021. (Erin Scott/Bloomberg)

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Lander had earlier apologized to his staff for speaking to them in a "disrespectful and demeaning way," according to an email obtained Monday by Fox News.

"The president accepted Dr. Eric Lander’s resignation letter this evening with gratitude for his work at OSTP on the pandemic, the Cancer Moonshot, climate change, and other key priorities," White House press secretary Jen Psaki said in a statement. "He knows that Dr. Lander will continue to make important contributions to the scientific community in the years ahead."

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Eric Lander participates in a swearing-in ceremony with U.S. Vice President Kamala Harris in her ceremonial office in the Eisenhower Executive Office Building on June 2, 2021, in Washington, D.C

Eric Lander participates in a swearing-in ceremony with U.S. Vice President Kamala Harris in her ceremonial office in the Eisenhower Executive Office Building on June 2, 2021, in Washington, D.C. (Anna Moneymaker via Getty Images)

Psaki had earlier deflected questions Monday regarding why Lander had not been fired, given Biden's promise on his first day in office to immediately fire anyone who treats colleagues disrespectfully.

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"If you are ever working with me and I hear you treat another colleague with disrespect, talk down to someone, I promise you I will fire you on the spot. On the spot. No ifs, ands or buts," Biden said.