Was Donald Trump 'blocked' from using the nuclear codes against Iran?

Former CIA analyst Larry Johnson alleged on a podcast this week that President Donald Trump wanted to use the nuclear codes against Iran during an emergency White House meeting, but that he was stopped by General Dan Caine, Chairman of his Joint Chiefs of Staff. He described the interaction as "quite the blow up." It comes as concern mounts over the US President's unpredictable behaviour, as many lawmakers voice doubt about his mental state.