Hillary Clinton went through even more vetting than Obama, McCain, Biden, Giuliani, Romney, etc. She's been being "vetted" by the American media -- not to mention Kenneth Starr -- since at least early 1992.   And she got the votes of 18 million Americans for the Democratic Presidential nominee.
It's not that the voters rejected Clinton -- any more than her supporters necessarily "rejected" Obama (or Edwards or Biden or Kucinich, etc.). Obama just had more support.