WASHINGTON — When is a gaffe not a gaffe? When Donald Trump says it. Over a period of 72 hours earlier in the month, the Republican front-runner faced a campaign crisis after unrest at his events forced him to cancel a rally in Chicago. He responded, not by apologizing but by justifying his supporters’ violent reactions to protesters at his events and offering to pay legal fees. Meanwhile, Hillary Clinton spent much of the same period cleaning up misstatements about former first lady Nancy Reagan’s role in addressing the AIDS epidemic, whether her policies would kill coal-mining jobs and her husband’s 1993 health care plan. The three-day window offered a glimpse into an extraordinary campaign cycle, in which strategists on both sides are wondering whether Trump’s penchant for provocation has shifted the gaffe gauge in American politics. His bombast already has shaken up the Republican primary contest.