GRINNELL, Iowa - Remember the story of the college sophomore who asked a planted question to Senator Hillary Rodham Clinton?

There she was, standing a stone's throw from Senator Barack Obama at a rally here tonight at Grinnell College. When it came time to take questions from the crowd, Mr. Obama smiled as he made a reference to the incident, assuring his audience that his questions were not prearranged, predetermined or planted.

As he shook hands along the rope line, he paused to talk briefly with her. In a quiet voice, she asked about the trajectory of his political career. Leaning close, he said, "I lucked out," before ticking through his path: long-shot Senate candidate, keynote speaker at the Democratic National Convention and, now, a presidential candidate.