Exactly what it says on the tin. Despite his disastrous 2008 campaign for the presidency, back in 2000, McCain was perceived quite differently. In fact, polls from his primary campaign showed him defeating Al Gore in many states, including California, Illinois, and Vermont, doing substantially better than his nomination rival, George W. Bush. It's been theorized that McCain could have taken the Perot voters as well as the Republican base, winning in a substantial landslide.
But what's everyone else's take on matters? Could these numbers have held up until election day? Assuming John McCain wins the Republican nomination in 2000, how does his campaign go? Who becomes his running mate? And how well does he do in November that year?
(I assume one side-effect would be Joe Lieberman declining Gore's offer to join the Democratic ticket, not wanting to campaign, against McCain, a friend of his.)