The 12th Amendment says "no person constitutionally ineligible to the office of President shall be eligible to that of Vice-President."
Okay, so that means if you're not eligible to be president, you're not eligible to be vice president. Makes sense. What would be the point of electing a vice president who can't succeed the president in case of death, incapacity or vacancy?
But then Congress and the states added the 22nd Amendment in 1951 to prevent anyone from following the example of Franklin D. Roosevelt, who won four terms. That's where things get dicey. "No person shall be elected to the office of the President more than twice," the 22nd Amendment says.
On its face, that seems to suggest that Clinton could be vice president because he is only barred from being elected president a third time, not from serving as president.
"In preventing individuals from being elected to the presidency more than twice, the amendment does not preclude a former president from again assuming the presidency by means other than election, including succession from the vice presidency," [Scott E. Gant, a partner at Boies, Schiller & Flexner in Washington, and Bruce G. Peabody, an assistant professor of political science at Fairleigh Dickinson University in New Jersey] wrote. "If this view is correct, then Clinton is not 'constitutionally ineligible to the office of president,' and is not barred by the 12th Amendment from being elected vice president."
"My tentative answer is that 'eligible' roughly means 'elected,' " [Eugene Volokh, a law professor at the University of California at Los Angeles ] wrote on his Web site, the Volokh Conspiracy, this summer, meaning that if Clinton cannot be elected president, he is no longer eligible at all.