What is the presidential "nuclear football"? Why a black briefcase always follows the president.

The Trump administration is coming under fire after a civilian guest at Donald Trump's Mar-a-Lago resort posed for a photo with the "nuclear football" briefcase and posted it to Facebook.

The Mar-a-Lago member, Richard DeAgazio, also posted photographs showing the president, his top aides and Japanese Prime Minister Shinzo Abe conferring about North Korea's missile test Saturday night on the club's terrace — before a dining room of civilians. DeAgazio has since deactivated his Facebook account.

While the photographs do not seem to violate Defense Department regulations, according to the Washington Post, it is unusual — and raises concerns about the administration's handling of classified material. 

What is the "nuclear football"?

The "nuclear football" is a black briefcase containing nuclear attack plans and other information needed in an emergency. It dates back to at least the Cuban Missile Crisis during the Kennedy administration, and is always with the president, carried by one of a handful aides authorized to handle it. 

At a campaign rally last August, former Vice President Joe Biden pointed out an aide who was apparently carrying the briefcase, drawing reproof from some in the conservative media — including Breitbart, which was helmed by Steve Bannon, now Trump's chief strategist. 

But military officials do not appear to be concerned about DeAgazio's photo with the aide carrying the football. The bigger issue, Naval War College professor Tom Nichols tweeted, was that the president and his aides had coordinated their response to the North Korean missile test in public view and not in a secure private location.