When I was in high school, a boy I knew joined the Marines and eventually went to Vietnam. We began writing to each other, starting when he was training to be a soldier and extending through two tours of Vietnam. One of the most memorable things he told me, early on, was that they were being taught to hate the Vietcong. They were encouraged to call them Gooks and other dehumanizing names; they were told over and over that these men — the men they would be fighting — were the lowest life form and needed to be taken out. My friend understood well the reasoning behind the training. He told me that if you believe someone is worthless, you’ll have no problem killing them.

Here is a taste of Donald Trump’s rhetoric toward journalists when he was campaigning: “They are the lowest form of life.” “I hate them.” “They are the enemy of the people.” Other words he used to describe the men and women who he believes make up “the fake media” (which means everyone but Brietbart and Fox News) have been: “Disgusting,” “irrelevant,” and “pure scum.”

If you don’t think his words resonated and were infectious, consider this — at one of his rallies, a man was seen wearing a T-shirt that read: “Rope. Tree. Journalist. Some Assembly Required.”

And if you don’t believe that words are the seeds from which actions sprout, think hard about the recent incident in which Republican candidate Greg Gianforte, on election eve for a congressional seat in Montana, body-slammed the reporter Ben Jacobs who simply asked him a legitimate question about health care. Think also about the deafening silence from Republicans on Capitol Hill. Well, except for Texas Governor Greg Abbott, who joked about shooting reporters. Brandishing his bullet-scored target at a shooting range he said, “I’m gonna carry this around in case I see any reporters.”

Violence doesn’t spring up in a vacuum. It doesn’t form itself from empty air. It is assembled, composed. It starts with words. My friend from long ago was right — if you believe that a group of people are without worth — if they are, as Donald Trump also said about the media, “the lowest form of humanity,” then you can do anything to them and feel justified. Violence, like oppression and tyranny, is a process.

Justice William O. Douglas wrote: “As nightfall does not come at once, neither does oppression. In both instances, there is a twilight when everything remains seemingly unchanged. And it is in such twilight that we must all be most aware of change in the air — however slight — lest we become unwitting victims of the darkness.”

We are in a time of ominous twilight right now. Darkness hovers beyond that, and there are those in power who are trying to lead us into it.