Where are you getting that 70%+ number?
Rasmussen never had him above 65%.
While Gallup had him at 68 and 69% during his first four days of usurpation, he has basically gone down hill from there.
USA Today/Gallup 1/9-11/09 - 83%
http://www.pollster.com/blogs/2009_01_09%20Topline.pdf
CNN 1/12-15/09 - 84%
http://www.cnn.com/2008/POLITICS/12/24/obama.approval/index.html
Post/Post 1/13-16/09 - 80%
http://www.washingtonpost.com/wp-srv/politics/documents/postpoll011709.html