How do you estimate the probability of a nuclear incident resulting from the current US actions?
Ideally, use a betting prediction market. But since this is probably not what you meant here are my guesses:
The odds of Russian intervening militarily = 40%.
The odds of the Russians losing the conventional battle (perhaps because of NATO intervention) conditional on them entering = 30%.
The odds of the Russians resorting to nuclear weapons conditional on them losing the conventional battle = 20%.
A Dan Carlin Podcast about how the United States is foolishly antagonizing the Russians over Ukraine. Carlin makes an analogy as to how the United States would feel if Russia helped overthrow the government of Mexico to install an anti-American government under conditions that might result in a Mexican civil war. Because of the Russian nuclear arsenal, even a tiny chance of a war between the United States and Russia has a huge negative expected value.