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He said the broken two-party system drives away good politicians and speculated that there is no clear next generation of third-party candidates to groom because “they don’t want to get their hands dirty.”

He said a billionaire such as New York Mayor Michael R. Bloomberg mounting a third-party bid might be able to move the needle in a way similar to how Ross Perot did in 1992, but even that would be a difficult feat.

Mr. Perot’s 19 percent showing that year helped Bill Clinton defeat President George H.W. Bush.

Mr. Nader won 2.7 percent of the national vote as the Green Party candidate in 2000, but he won 0.3 percent as an independent in 2004 when he appeared on the ballot in only 34 states.