Donald Trump has secured a unique place in the history books as the first president in American history to be impeached twice. What that means in practical terms isn't clear. There’ll be no Trump trial in the Senate before Joe Biden moves into the White House, but Democrats insist he will be held to account for the assault on the Capitol. Stephen Sackur speaks to the veteran lawyer Alan Dershowitz, part of the defence team in the first impeachment. Will he get involved in the sequel, and how will it play in a divided America?