From left: Donald Trump, Bill Weld, Mark Sanford and Joe Walsh. (Photo illustration: Yahoo News; photos: AP, Bill McCay/Getty Images, AP, Tom Williams/Roll Call via Getty Images)
Incumbent presidents have not infrequently faced primary challenges from members of their own party. In 1976, former California Gov. Ronald Reagan sought to replace President Gerald Ford on the Republican ticket. Four years later, former Sen. Edward Kennedy took on President Jimmy Carter, and in 1992, hard-right pundit Patrick Buchanan mounted a campaign against President George H.W. Bush. But none of the incumbents agreed to a primary debate.
Gov. Bill Weld
Canceled primaries? What are you afraid of, Mr. No-Show? Intelligent, experienced, honest and decent competitors? Now more than ever, @realDonaldTrump, you can run but you cannot hide. #LetTheGamesBegin