After Ashoka's death, a series of less-skilled emperors came to power. These emperors changed some of their policies. They were less accepting of other religions, and some did not respect Hinduism. The empire was divided, and local leaders took more control. Invaders from northern kingdoms attacked the divided empire, further weakening it. By 180 BCE, just 50 years after Ashoka's death, the empire had broken into many smaller, independent kingdoms.
The answer is: to act as a ceremonial role within the Senate.
The phrase 'Pro Tempore' is a latin language with the meaning of 'for the time being'. President pro tempore of the senate only elected as a ceremonial role when the actual presiding officer of the senates is unable to attend the meeting/conference.
