We find it arithmetically very difficult to construct scenarios in which asset returns are at their historic average values and real G.D.P . growth is markedly slowed , '' wrote the economists , Paul Krugman of Princeton University , whose Op-Ed columns in The New York Times have long been sharply critical of Mr. Bush 's plan ; J. Bradford DeLong of the University of California , Berkeley ; and Dean Baker of the Center for Economic Policy and Research , a liberal research organization in Washington .