How have third-party candidates impacted the national popular vote since the 1970s?

Since the 1970s, third-party candidates have sometimes received enough votes to affect which major-party candidate wins, even though they have not consistently won a large share of the vote. When their support draws voters away from a major-party candidate, they can act as “spoilers.” So the correct choice is B: they have occasionally gained enough support to act as spoilers.

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