'Decades of polarization have fuelled a perfect storm in which violence has become endemic'

The man charged with killing one Minnesota lawmaker and wounding another meticulously planned the shootings and intended to inflict more carnage against those on his hit list, driving to the homes of two other legislators on the night of the attacks, a federal prosecutor said Monday. We speak to historian Matt Dallek, Professor of Political Management at George Washington University, about the rise of political violence in the United States.