If you want to write about the United Nations these days, you need a thick skin.

The Trump administration’s decision to cut funding to the U.N. in its first proposed federal budget, announced last week, has unleashed a vitriolic argument in the U.S. about the organization and its values. This is not new. The American left and right have long debated the U.N. in heated terms, often with little reference to what it really does. ...