Transparency is a popular word in this presidential election, with all three candidates finally having released their tax returns. Yet the public still hasn't seen the records of an institution with some of the biggest potential for special-interest mischief: The William J. Clinton Foundation.

Bill Clinton established that body in 1997 while still President. It has since raised half-a-billion dollars, which has been spent on Mr. Clinton's presidential library in Arkansas and global philanthropic initiatives. The mystery remains...