The Sideshow sums it up pretty well. An excerpt:
The Bush “message” was that everything Americans wanted – education, prescription drug benefits, Social Security, paying down the debt, balancing the budget, etc. – would be preserved by both candidates. Bush openly lied in the debates about his polices and his numbers in order to sound as much like Gore as possible, claiming that under no circumstances would his tax cut (and revival of Star Wars/SDI) threaten any of those programs. In many respects, you could say that Bush managed in the end to stay even in the polls largely by pretending to be a slightly more personable and honest carrier of Gore’s message.
Polls of undecided/swing voters after the election consistently showed that the single greatest reason given for voting for Bush was a belief that Gore was not honest. Many people clearly believed that there was no substantive difference between Gore and Bush on policies – it was just a matter of degree – but that the real distinction was one of character, an area where the RNC spin had “proven” that Gore fell short.