On one level, the BBC made some pretty evident mistakes on impartiality - and most damagingly on a documentary on Trump, the echoes of which quickly reverberated across the Atlantic. And as a result, Tim Davie, the Director General had to resign. But there's a lot more to the story than that - and the truth is that the institution has been under attack for the last few years as political polarisation has made its mission increasingly impossible. Let's discuss.