Presidential candidates are a breed apart, often propelled by traits that have shaped their careers and have deep roots in personal histories.

Often their greatest strength can turn at supernova speed into their greatest weakness. The exact qualities that set them apart from the field trip them up eventually over the long haul of a presidential campaign.

Florida Sen. Marco Rubio is a man in a hurry, whose dizzying political ascent—he has never lost a race—is a testament to his quickness to spot openings and go for them. The question now, as he aims for the White House, is whether voters ultimately see Rubio as refreshing and bold, the inspiring face of a new generation—or just a promising young pol getting ahead of himself.

In this series of eBooks, The Washington Post is exploring in-depth all these key characteristics of the leading presidential contenders, the very characteristics that could help make one of them the country’s next commander in chief—or forever sink their presidential ambitions.