One can argue that you should be respectful to secular kings, especially ones who aren’t especially antagonistic me – and that American presidents should be considered in that class (though the job is more like a British prime minister, since under American law either the Congress, or perhaps the “people” and “states” fill the legal position that the “Crown” fills in the British system).
However the mayor is merely the employee of the people, and especially for one who is clearly antagonistic to frum Jews, calling him nothing worse than “Bloomy” is showing moderation.