Hillary Clinton fell short of political immortality in her quest to be the first woman president, but she is relishing the "18 million cracks" she punched in America's highest glass ceiling.  As she shelved her campaign, and admitted defeat for her hopes for a return to the White House in her own right, Clinton could take consolation in her new status as a pathbreaking, historic figure.  "If we can blast 50 women into space, we will someday launch a woman into the White House," she told 2,000 supporters who turned up to see her endorse Democratic rival Barack Obama, the presumptive party nominee.  "Although we weren't able to shatter that highest, hardest glass ceiling this time, thanks to you, it's got about 18 million cracks in it," she said, referring to her tally of Democratic nominating votes. "And the light is shining through like never before, filling us all with the hope and the sure knowledge that the path will be a little easier next time."