I don't know how untouchable US citizen ever were, but there has been a change in perception over the last couple of decades. Some of it has to do with political actions or inactions, but I think big part is just due to information becoming more easily and quickly available worldwide, the facade of the "american dream" started crumble. So I think for the most part it just that US citizens in a foreign nation simply aren't considered special anymore and in many parts of the world the perception shifted from generally positive to negative. But this is not just since Trump took office as I have heard some people think. Neither with the military power and fear thereof.