With Kaine's selection for VP, Hillary signals a campaign emphasizing the choice between compassionate, intelligent stability versus a raving, bigoted, dangerous madman. You might not agree with either of those characterizations, but I believe it's the theme they'll hammer relentlessly.
How will it go? In Trump's favor: he has an acute, intuitive grasp of the current white, middle class weltanschauung. In Hillary's favor: she has an almost excessive discipline and very smart campaign technicians.