US President Donald Trump seems determined to ignore mounting evidence that Saudi Arabia's Crown Prince Mohammed bin Salman ordered the murder of journalist Jamal Khashoggi.

In the face of a leaked report from the CIA naming bin Salman, or 'MBS', as the man who gave the order, the President has doubled down, stressing the prince told him at least five times that he wasn't involved.

So why is the President so keen to protect this one ally? And what do we know about Saudi Arabia's 33-year-old leader in waiting?

Today on The Signal we speak with New Yorker magazine correspondent and senior fellow at the Woodrow Wilson Center Robin Wright, who worked with Khashoggi.

We also hear from Curtin University lecturer Dr Ben Rich, and Griffith University Associate Professor Halim Rane.