I participated in one of the marches. It was exhilarating, peaceful, hopeful. I wasn't thrilled when I heard Madonna hurl the F-bomb, as I wasn't when Trump hurled it several times while campaigning in New Hampshire. (David Ortiz gets a pass from me, but that's a different subject.) 
The reason for my post, though, is to agree that a threat of violence, even implicit, even in some sort of jest, against the president is never acceptable. I am certain that Madonna's remark about "blowing up the White House" will be investigated. It should be, as were Trump's implied threats against Hillary Clinton ("Second Amendment remedies.")
The marches on Saturday were a wonderful expression of commitment to peaceful political action. I was in a crowd of 175,000 people and at one point I was walking against the flow of the crowd. Not a shove or even a bump -- not even an arrest anywhere in the crowd.
What Madonna said, in my view, was not worthy of the event -- but also not representative of it.