She is the first congressional representative to wear a scarf around her head, and that scarf is for some a symbol of the breadth and depth of our acceptance of others. For others, it is a symbol of alienation and rejection of the America she claims — simply by holding office — to represent. To those who see her this way, the hijab or head covering is seen as a hostile schmata (rag) whereby she is not merely carrying on one of her subculture's customs, but, in essence, giving the finger to the country she now would participate in governing.
I think I can bury my head in the sand about Omar, because the House of Rep is filled with fringe freaks on both sides. They don't really matter.
I think the MAGA caps are perceived as giving a finger to America by many Americans too.