How exactly does Donald Trump propose to make the American economy great again? By junking the economic orthodoxies of the recent past, it seems. He wants to slash taxes, spend big on public projects and renege on trade deals that he claims rip America off. Stephen Sackur talks to one of America's most respected economic analysts, Mohamed El-Erian, formerly CEO of PIMCO investments. What will Trump's brand of interventionism do for the US and world economies?