Each largely undefined candidate will get a chance to make a mark.
Pence is Donald Trump's running mate and he's taken a decidedly un-Trump-like approach — he prepared for the event with mock debates and numerous study sessions.
Kaine is Hillary Clinton's running mate and he's been cramming, too.
Voters always have a reason to size up running mates.
The 2016 presidential candidates are older than the norm. Though their doctors say they are fit to serve, Hillary Clinton will be 69 before the election and has had several health problems in recent years. Donald Trump is 70 and held off disclosing much about his fitness.