For many people I work with, even visiting the US is something they're trying to avoid.

I can confirm, I'm definitely thinking twice before visiting my friends and coworkers in the US again, and I'm positively not going to book a flight that goes through the US when flying to another American country (eg Canada).

Even for many Americans living overseas, visiting the US requires more to think about than before.

I second that.

take a random sample of 100 devs in Ukraine and India and offer them a green card to the US of A. how many do you think would take it? and for people who wouldn't, how many do you think would cite Trump as their reason?

That's not a good question. There have always been people who wouldn't have wanted to move to the US, for various reasons. People usually like to stay at home, in a culture they're familiar with, near people they know, unless something really pushes them to leave.

A better question is: take a random sample of 100 devs in Ukraine and India in early 2016 and offer them a green card, and then do the same today. How do the numbers compare? Now you're seeing how many people would have liked to come here, and now have changed their minds because of recent political events.

Many would take it, no question. However, taking a green card doesn't necessarily mean that the person will stay in the US forever. The American culture and lifestyle is rather specific and not for everyone. It requires living in the US to start realizing it. You can't grasp it from abroad. Some developers return to Ukraine/India and feel happier there.

Well, it really depends on where you are moving from, doesn't it?