Decision 2012: Ryan and Rice Energize GOP Convention Crowd

Assuming what has become a traditional "attack dog" role for presidential running mates, Congressman Paul Ryan accepted the Republican nomination for vice president with a convention speech accusing President Barack Obama of failing to lead the country.

Class discussion: Why do vice presidential candidates lead the attacks on the opposition? Does it really help their running mates appear more "presidential" and above the fray? When did vice presidential candidates start assuming their aggressive role in campaigns?