Despite saying that he believed Mr Obama would defeat Senator John McCain, his Republican rival, in the election in November, the former president refused to say that the presumptive Democratic nominee was ready for high office.
"You can argue that nobody is ready to be president," Mr Clinton told ABC News. "You can argue that even if you've been vice-president for eight years, that no one can be fully ready for the pressures of the office."
Asked the question again, he responded: "I never said he wasn't qualified. The constitution sets qualification for the president. And then the people decide who they think would be the better president. I think we have two choices. I think he should win and I think he will win."