Demonstrations by white supremacist groups on August 12 turned deadly after a neo-Nazi ploughed a car into a crowd, killing one counter-protester and injuring at least 19 other people in Charlottesville. Two police officers were also killed when their helicopter crashed.

Trump’s initial response was widely criticised, even by some members of his own political party, for being insufficient and vague. Though the president later condemned the hate groups, he went on to effectively undo his conciliatory remarks by giving an off-the-rails news conference days later in which he once again blamed “both sides” in Charlottesville.

Kammen, who was appointed during Barack Obama’s presidency, said it would be unconscionable for him to continue serving the administration after those remarks. He said he stood with “the unequivocal and authoritative statements” of a slew of other public officials, both Democratic and Republican.

“Acts and words matter,” Kammen wrote. “To continue in my role under your administration would be inconsistent with the principles of the United States Oath of Allegiance to which I adhere.”

However, his most biting message may have come in the form of a hidden acrostic; the first letter of each paragraph spelt out “I-M-P-E-A-C-H.”

The State Department appointed Kammen, an energy professor at the University of California, Berkeley, as one of five US science envoys in March 2016. At the time, Kammen said he would be working on various global energy initiatives, as well as “the wider Paris Accord.”

In his resignation letter, Kammen also cited other concerns that predated Trump’s Charlottesville comments, including the president’s decision to withdraw from the Paris climate accord in June.

“Particularly troubling to me is how your response to Charlottesville is consistent with a broader pattern of behaviour that enables sexism and racism, and disregards the welfare of all Americans, the global community and the planet,” Kammen wrote. “Your decision to abdicate the leadership opportunities and the job creation benefits of the Paris climate Accord, and to undermine energy and environmental research are not acceptable to me ... Your actions to date have, sadly, harmed the quality of life in the United States, our standing abroad, and the sustainability of the planet.”

According to his letter, Kammen has also served in various federal roles since 1996, including at the Energy Department and the Environmental Protection Agency.

“Today, Dr Daniel Kammen made a personal decision to resign. We appreciate his dedicated service to US scientific diplomacy during his appointment working on energy efficiency and renewable energy in Africa as a Science Envoy,” a State Department representative said.

Last Friday, the members of the President’s Committee on the Arts and the Humanities announced they were resigning en masse in a fiery letter.

“Ignoring your hateful rhetoric would have made us complicit in your words and actions ...” the letter stated. “Supremacy, discrimination, and vitriol are not American values. Your values are not American values. We must be better than this. We are better than this. If this is not clear to you, then we call on you to resign your office, too.”

That letter also contained a hidden message. The first letters in each of those paragraphs, taken together, spelt out: “R-E-S-I-S-T.”