This rather splendid (and splendidly brief) video from Vox is a gift to US politics junkies. With the Iowa Caucus date of Feb 1 closing in, it's worth a watch if you want to understand how the Democrats and Republicans in this Midwestern state will decide their respective favourites in the presidential race, and why it matters.
You may also be interested in
800,000 polling stations, six million election workers, and the most complicated single-day ballot in global history.