Eight years in the No. 2 spot is enough for Al Gore.
The former vice president, who issued a challenge to the next President of the United States on Thursday to make the country's electricity output carbon-free in 10 years, said later that he will not under any circumstances serve as Barack Obama's running mate.
Unlike the office of the presidency, there are no imposed term-limits on the second highest office in the land. But Gore, who considerably expanded the role of vice president, said he's imposing his own term limits on the job.
"I have a personal term limit," he told CBS News Thursday. "Only two terms as VP."