There is something very off here; every group of scientists I know is mostly liberal, in the classic sense; many rubbed shoulders with the likes of Bernie Sanders in the Civil Rights era. The issue runs deeper, in the under-representation of people of color * (unless you are from India or Asia) in the sciences. Implying that whites are more interested in their own fashion movements de jour than in the problems of other communities is really an insult to the intelligence and sensitivity of the scientific portion of our adult population — which not coincidentally voted overwhelmingly against the most unintelligent and uninformed president in over a hundred years.
This story, even at face value, is one anecdotal event, saying more about the D.C. police than the immediate group around him. No such conflict was noted at the event I attended, and I am very sure the crowd would not have stood apart, had that happened.
Scientists are not, by nature, joiners; they are introspective, devoted to nuance and adverse to broad generalizations. The diversity of handmade signs seen reflect this in originality and awareness that appalling numbers of programs, budgets, research agencies are threatened by ignorant de-funding which will have lasting negative impacts for decades. Imagine that Flint Michigan was still unaware of the water contamination crisis, and you see just one small example of the interrelated social and scientific battles we live with daily.