This may be one of the most cynical ploys in US politics I ever read about. And I read a lot.
New York Times, White House Helps Block Extension of Tax Cuts: The White House helped to block a Republican-brokered deal on Wednesday to extend several middle-class tax cuts, fearful of a bill that could draw Democratic votes and dilute a Republican campaign theme, Republican negotiators said
In other words, the only reason Bush & Co. support tax cuts is to use them as a wedge issue. Give them the tax cuts they ask for bipartisanly, they not only lose interest, but scupper it.
Fortunately, if recent polls are to be believed, President Lincoln was a better judge of the American character than PT Barnum.
Update: Apparently, PT Barnum may never actually have said that there's a sucker born every minute.