Washington (AFP) - A US government science envoy on Wednesday became the latest official to resign over Donald Trump's refusal to condemn neo-Nazis and the latest to send a coded message of defiance via his resignation letter.

Daniel Kammen, who had been in government service since 1996 and served as a state department envoy since 2016, said Trump had "harmed the quality of life in the United States, our standing abroad, and the sustainability of the planet."

But apparently it was Trump's equivocation about white supremacists' who led a deadly march in Charlottesville, Virginia that was the final straw.

"My decision to resign is in response to your attacks on the core values of the United States. Your failure to condemn white supremacists and neo-Nazis has domestic and international ramifications," Kammen wrote.

But within the one page letter was a less obvious message -- an acrostic, with the first letter of each paragraph spelling "IMPEACH."

Kammen is the latest in a series of officials and panelists to resign their posts -- from members of the arts to business leaders -- and is not the first to deliver a hidden message in doing so.

When the President's Committee on the Arts and the Humanities resigned en masse last week, the first letter of each paragraph of their letter spelled out "RESIST" -- a watchword for opponents of the Trump administration.

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