It depends on what you mean by nuclear war. And what timeframe.
If you mean at least one nuclear weapon detonated in anger within, say, the next three years and three months then I'd say higher than it's been in my lifetime. Trump, plus Kim, plus India-Pakistan tensions, general global situation and an incompetent President... fifteen percent. (Which seems really scary high!)
If you mean Global Thermonuclear War then under one percent. The only one who really might start that would be Trump. And I'm enough of an optimist to think the people around him would stop him first, one way or another.
I agree with these numbers. About 15% for a limited nuclear exchange, very low for civilization-ending catastrophe.
