During most campaigns, the job of the vice-presidential candidates focuses on boosting the person heading the ticket. Proving their suitability for the top job is secondary. But this year is different. The president is 74 and spent much of the past week in the hospital, and his Democratic rival is 77. So it was vital for their running mates, Vice President Mike Pence and Senator Kamala Harris, to show in Wednesday night’s debate that they would be capable of stepping up if necessary. We speak to Alexander Burns, a Times national political correspondent, about the candidates’ strategies and whether anything new emerged four weeks before the election. Guest: Alexander Burns, a national political correspondent for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily  Background reading: The back-and-forth between Vice President Mike Pence and Senator Kamala Harris was more civil than the unruly presidential event, but featured sharp exchanges ov...