The major networks have lined up their top anchors and cleared their schedules. CNN has been running a countdown clock for the past 24 hours.

Washington will come to a standstill when James Comey, the former head of the FBI, testifies before the Senate intelligence committee on Thursday morning about his investigation into potential links between Russia and the Trump election campaign.

Pundits have taken to describing it as Washington's Super Bowl and comparing it with the Watergate hearings the brought down Richard Nixon.

But no-one knows exactly what Mr Comey will say. Will he accuse Donald Trump of trying to obstruct his investigation? And how much will he reveal about the probe itself?

Why is he testifying?