It has become one of Hillary Clinton's most effective attack ads: Donald Trump is shown boasting to David Letterman during a 2012 Late Show appearance that his top-selling neckties and shirts are made "somewhere" — until Letterman points out they're actually manufactured in China and Bangladesh.

Just one problem: the Clinton campaign never got permission from Letterman or his Worldwide Pants company to use the 25-second clip. Lawyers who consulted with THR are split on whether the use of the footage (owned by Worldwide Pants, not CBS) would be a "fair use," but the issue probably is moot: Letterman is a big Clinton supporter and likely would have given permission — if he had been asked. A rep for Letterman declined to comment.

This story first appeared in the Sept. 9 issue of The Hollywood Reporter magazine. To receive the magazine, click here to subscribe.