Every four years, a disproportionate amount of attention is focused on the unlikely midwestern state of Iowa. In a very real way, the Iowa caucuses encapsulate the profound political and ethical challenges that confront the Democratic Party in its bid to defeat Donald Trump in November — challenges that continue to bedevil democratic politics in other countries: How to mobilise voters around a common cause, without tipping over into either absolutism or unprincipled, 'whatever-it-takes' pragmatism?