Michael Eisen, an evolutionary biologist, is among the elite of American scientists, with a tenured position at the University of California, Berkeley, and generous funding from the Howard Hughes Medical Institute for his research on fruit flies.

But late last month, dismayed over the Trump administration’s apparent disdain for evidence on climate change and other issues, Dr. Eisen registered the Twitter handle @SenatorPhD and declared his intention to run in the 2018 election for a seat in the United States Senate from California. His campaign slogan: “Liberty, Equality, Reality.”

“I’m not sure I’m the best vehicle for this,” said Dr. Eisen, whose professional attire consists of shorts and T-shirts bearing mottos supporting open access to scientific literature, a cause he has championed. “But if we want to defend the role of science in policy making, scientists need to run for office.”

Since Mr. Trump’s election, many other scientists have expressed concern about rumors and public statements on the new administration’s views on science, climate change and the role of federal offices like the Environmental Protection Agency.