Pundits often note that George Bush was the first sitting vice president to win the White House since 1836. What they seldom mention is that few of them even tried. For most of our history the vice presidency was filled by stand-ins and mediocrities. So long as the president didn't die in office the vice president simply walked off into obscurity when his time was through. Today a veep is a likely successor, or at least a future party nominee.
Voters know that, and they see the candidate in that light.
The bottom line is that the nominee and the veep should be a unified team. It gave the Democratic ticket a coherent and unified message, and it signaled on Clinton's part a confidence about who and what he was. That's exactly what a modern vice-presidential pick should do. And Gore fit the bill. Here's why Kerry does the same for Gore.