Only on the "CBS This Morning" podcast, CBS News political correspondent Ed O'Keefe talks with Iowa-based CBS News campaign reporters Musadiq Bidar and Adam Brewster about what they've learned while traveling more than 20,000 miles each throughout the Hawkeye State. They discuss the issues that Iowa voters are most passionate about how the caucus system works. Plus, Bidar and Brewster explain which candidates have built the strongest campaign infrastructures in the state, how the race has evolved since the summer and why it's important for a candidate to do well in Iowa.