Four years ago, Carl Icahn quietly slipped out of Donald Trump’s raucous presidential election victory party at the New York Hilton. It was 2am, markets were tanking on the shock outcome, and the billionaire investor wanted to take advantage. 

Hillary Clinton’s loss to the bombastic property developer had sent US stock market futures tumbling as much as 5 per cent that night, triggering trading curbs designed to damp crashes. 

Around the world, investors were scrambling to understand what one of the most sensational upsets in US election history meant for their own markets. But Mr Icahn was so sure that Mr Trump’s presidency would be a boon to the economy that he called his brokers and placed an audacious $1bn bet that the stock market would recover from the fright.