Possible Clues:

• Two-and-a-half presidential terms
• Went off, it's said, over a number of years
• Decennium
• The '70s, e.g.
• Wasted away, we hear, over a number of years
• X y !
• It takes years for this to have rotted, by the sound of it
• Period just short of 26 years? Sounds bad
• Group of ten became rotten, we hear
• The noughties, say