It is visible as the pubic hair has become so vast that trying to hide it under normal clothes is comparable to hiding Jimi Hendrix's afro under a swimming cap.
Many experts have speculated that Bush was wearing a "Personal Cueing Device", or what newscasters and movie makers call an IFB. A company called Comtek makes an IFB system which matches the size of Bush's mysterious bulge.
A wireless IFB (like the Comtek) consists of a hidden radio receiver worn on your person which then relays audio to a small earpiece which fits entirely in the ear (like a tiny hearing aid). Prepared lines or "cues" which are to be spoken are then transmitted to the device wearer.
There have been other times that Bush has been spotted with this and other mysterious bulges, such as when he has had important speaking engagements, or meetings with important world leaders.
For a complete explanation of how this system works, do a Google search on these words: Comtek IFB