Gun violence is a fixture in American life - but the issue is a highly political one, pitting gun control advocates against people who are fiercely protective of their right to bear arms. Every mass shooting in the U.S. raises calls for better policies to prevent such tragedies. There's evidence suggesting that certain kinds of laws may reduce deaths from mass shootings, say scientists who study the field — but those policy options are not the ones usually discussed in the wake of these events. What are we to do?