I did a visual review of the history of this poll back to his inauguration. He peaked at +30 two days after his inauguration, and it’s been essentially downhill since then. His lowest was -24 on September 9, 2010. The last time he had a positive rating was June 29, 2009, just 5 months after his inauguration and peak. So in the space of just over 14 months he had a swing of -58.
Sorry, my calculator is acting up. The swing was -54. ;-)