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The day Donald Trump took office as US president, the mood was sombre at the main research campus of the Environmental Protection Agency (EPA) in Durham, North Carolina. As scientists arrived for work, they saw pictures of former president Barack Obama and the previous EPA administrator, Gina McCarthy, coming down off the walls. Researchers had reason to be anxious: Trump had threatened many times during his campaign to shutter the EPA, and he had already taken steps along that path. Weeks before he moved into the White House, Trump had nominated Scott Pruitt to head the agency — a man who had spent his career filing lawsuits to block a variety of EPA regulations.