President Barack Obama is like a guy who sneaks onto a marathon race course a mile or so from the finish line and pretends he ran the whole thing. In his speech Tuesday night commemorating the return to the United States of the last American combat brigade in Iraq, Mr. Obama patted himself lustily on the back for not screwing up a self-imposed timetable for withdrawal of U.S. forces that was made possible by the policies of President George W. Bush.