The 25 Most Influential Works of American Protest Art Since World War II...the question of what, precisely, constitutes protest art is a thorny one — and we kept tripping over it. Is it a slogan? A poster? Does it matter if it was in a museum, in a newspaper or out on the street? Does impact matter? Did it change what you think or believe? Must it endure? What does that mean? And what is the difference, anyway, between protest art and art that is merely political?