Here is one  poll:

Gallup finds that Hillary supporters are more likely than Obama supporters to bolt to McCain if their candidate isn't the nominee. Yet a significant percentage of Obama supporters --19%-- say they would defect, too.

And here is another:

Poll Tracker

    *
      Pres '08 (D)
      Mar 26 Gallup
      Obama 47%, Clinton 46%
    *
      Pres '08
      Mar 26 Gallup
      McCain (R) 46%, Obama (D) 44%
    *
      Pres '08
      Mar 26 Gallup
      McCain (R) 47%, Clinton (D) 45%
    *
      Pres '08 (D)
      Mar 26 Rasmussen
      Clinton 45%, Obama 45%
    *
      Pres '08
      Mar 26 Rasmussen
      McCain (R) 51%, Obama (D) 41%
    *
      Pres '08
      Mar 26 Rasmussen
      McCain (R) 50%, Clinton (D) 43%

There is a Democrat who was right about the war, who has won the Nobel Peace Prize and an Oscar, who might, if asked nicely, be willing to unite the Democratic Party and win the election in November. His name is Al Gore.
http://seaton-newslinks.blogspot.com/