Barack Obama's speech endorsing Hilary Clinton is being described as special.

The US President referred back to the convention speech he gave when he was vying for the top job himself.

His former speech writer David Litt says almost no one knew who he was at that time.

"He put forward this vision of America, and 12 years later after 8 years as President, he kind of went back to it and said this is why this vision still applies, and it's also why Hillary Clinton is the person to carry it forward.

LISTEN TO THE INTERVIEW WITH DAVID LITT ABOVE