As the presidential race heats up, vice-presidential expert Joel Goldstein discusses how the role of the nation's No. 2 has changed over the decades.
Marco Rubio? Nikki Haley? Chris Christie? Mitt Romney's VP choice is not just about ticket-balancing, which the evidence does not show as affecting election outcomes. Historical patterns show that with his pick for 'veep,' Romney will anoint a future presidential front-runner.