The quick and simple defense of his brother George W. Bush earned one of the loudest rounds of applause of the night. Aides said it was an impromptu decision spurred by an attack from Donald Trump, the GOP front-runner.

But those four words refocused a campaign in desperate need of a "moment," and signaled the extent to which Jeb Bush has become comfortable — even eager — to highlight rather than play down his family ties.

Those words also ignited a broader debate about George W. Bush's legacy and whether the former president kept the nation safe during his eight years in office, which included the attacks of Sept. 11, 2001, and the beginning of a war in Iraq that still reverberating a dozen years later.