Frost Over the World - Has US politics become too vitriolic?

Following a shooting at a political event in Tuscon, Arizona, Sir David talks to Laura Schwartz, an expert on the Democratic Party, Julian Zelizer, a professor of History of Public Affairs at Princeton University, and Republican commentator Charlie Wolf on whether US politics is becoming too vitriolic. Plus, economist Dambisa Moyo was named one of the world's 100 most influential people by Time Magazine and features in Oprah Winfrey's power list of "20 remarkable visionaries". She talks to Sir David about her new book, 'How the West was Lost'. And author and former New York Times correspondent Stephen Kinzer talks about how it is time for the US to engage with Iran and his new book, 'Reset the Middle East'.