So, an Illinois politician once said
"You can fool some of the people all of the time
And you can fool all of the people some of the time
But you can't fool all of the people all of the time."
In the newest issue of THE NEW YORKER (Jan. 19th 2009, page 22), Hendrik Hertzberg adds a little more precision, observing that
"you can fool some people all the time. We now know how many 'some' is: twenty-seven percent."
Update, Jan. 19:
Tonight on MSNBC they're reporting the results of a newer poll: the Incumbent's approval rating is now down to 22%.