It didn't begin with Trump. It being the truth that science has always been under attack to a greater or lesser degree. So, what is different today versus yesterday that causes scientists and their supporters to march?

Did you happen to see last year's 60 Minutes segment, "Dialing for Dollars"? "Nearly every day, [our elected representatives] spend hours on the phone asking supporters and even total strangers for campaign donations -- hours spent away from the jobs they were elected to do."  Industry has always had a heavy hand in influencing Congress and in attacking, delaying, or favoring selected scientific research.

Add Trump to the mix and it's easy to understand why scientists and supporters would march for science. Trump defines truth as whatever he says it is. That should be alarming to all of us.

If you are interested, this article provides a good overview of the forces attacking science:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1447376/