How do you explain the Lib Dems' stunning victory?

<div>In a political upset the Liberal Democrats have won the by-election in </div> <div>Chesham and Amersham in a massive poll swing from the Tories. And in other political the new DUP leader Edwin Poots has resigned, leaving his party to figure out what to do next. To dissect what happened, Cindy Yu is joined by James Forsyth and Katy Balls. </div>