When Harold Macmillan became Britain's prime minister in 1957, a reporter asked him what could blow his government off course. "Events, dear boy," Macmillan replied. "Events." American presidents of the last 50 years would have no trouble understanding that sentiment. It's unexpected "events" that often upend a leader's agenda. Bill Clinton arrived with an ambitious set of domestic goals but found himself quickly enmeshed in unexpected crises in Somalia and Haiti. George W. Bush's first year was overwhelmed by the terrorist attacks of Sept. 11, 2001. Barack Obama came to office amid a financial crash, then faced an oil well blowout in the Gulf of Mexico. And Donald Trump? Well, let's just say he was an ongoing crisis, often self-generated.