NEW YORK (AP) âÄî Presidential candidates John McCain and Barack Obama made ground zero their common ground for one rare day, free of politics and infused with memory. Putting their partisan contest on a respectful hold, they walked together Thursday into the great pit where the World Trade Center towers once stood and, as one, honored the dead from the terrorist attacks of Sept. 11, 2001. They walked down a long ramp flanked with the flags of countries, chatting at times, silent other times, and sharing a quick laugh at one point. Right behind them, Cindy McCain clutched Mayor Michael Bloomberg’s arm âÄî Michelle Obama was with her daughters in Chicago.