Final answer:
Ralph Nader's third-party candidacy drew votes away from Al Gore in the 2000 presidential election, particularly in key states, leading many to believe his candidacy cost Gore the election.
Step-by-step explanation:
Ralph Nader's candidacy in the 2000 presidential election had a significant impact, especially in influencing the type of campaign run by Democratic nominee Al Gore. Nader's focus on environmental issues and social justice drew votes from Democrats who normally would have voted for Gore. Many analysts suggest Nader's presence in the race, particularly in key swing states such as Florida, contributed to Gore's ultimate loss to Republican George W. Bush. This scenario is emblematic of the "spoiler effect" where a third-party candidate attracts votes from one of the major parties, potentially altering the election outcome.
In response to Nader's candidacy, Gore shifted his own platform to include stronger rhetoric against corporate excesses, attempting to appeal to the same progressive voters that Nader was attracting. Despite this tactical move, the close polls in key states such as Florida and the thin margins by which Bush won those states led to the perception that Nader's campaign indeed cost Gore crucial votes, confirming the role of third parties as potential spoilers in a tightly contested election.