The leader said recently that he's not afraid of a confrontation with America. Their slogan is literally "God is great, death to the U.S., death to Israel, curse the Jews, and victory for Islam."
I think they got quite a bit of courage from taking over half the country and showing themselves genuinely capable in war, but they clearly have absolutely no idea what a confrontation with America actually looks like. It's like going from high school football to playing in the NFL.