Despite Donald Trump leading in the polls, victory in the GOP presidential primaries isn’t certain. Ahead of the Iowa caucuses, Trump hopes to extinguish his opponents. But history has shown that not every winner in Iowa goes on to become the nominee.

The U.S., Yemen and the risk of regional escalation

Post Reports is the daily podcast from The Washington Post. Unparalleled reporting. Expert insight. Clear analysis. Everything you’ve come to expect from the newsroom of The Post, for your ears. Martine Powers and Elahe Izadi are your hosts, asking the questions you didn’t know you wanted answered. Published weekdays around 5 p.m. Eastern time.