What must always be within 12 metres of a U.S. President?

HER HUSBAND?

(just kidding...or maybe not!)

I cannot confirm the distance of 12 meters, but the memoirs of Robert S. McNamara suggest, "The president always had at hand nuclear release codes in the so-called football, a briefcase carried for the president at all times by a US military officer".

This reference speaks about the "... man who carried the "Nuclear Football", the black briefcase with the nuclear codes that accompanies the President wherever he goes".

http://www.globalresearch.ca/index.php?context=viewArticle&code=MCN20050506&articleId=149

http://mikesamerica.blogspot.com/2006_09_01_archive.html

Here's a worthless little factoid page that states:

QUESTION: What must always be within 40 feet (12 meters) of the sitting US President?
ANSWER: Case with the nuclear launch codes.

exquizzme.com/2007/11/129-just-in-case.html [no longer exists]

I think the 12m (40 ft.) part is probably not an official requirement. Everything I've read on it says it must be kept "near" the president. You can check out this article and its footnotes.

https://en.wikipedia.org/wiki/Nuclear_Football