Back in 2000 McCain and Bush were in a virtual dead heat through the first 6 states. Bush won Iowa's silly caucus but then McCain destroyed him in New Hampshire. It was a virtual coin flip in the weeks going into the super Tuesday (that was then held in March I believe) until Bush started really destroying McCain in a horrible mud slinging campaign. And McCain, like a loyal party member, bit his tongue about his true feelings about Bush when it was obvious that he was going to lose the Republican bid. If McCain had lashed out at Bush about how he felt about the man and his campaign, it would have given Gore the edge (of course Gore made plenty of mistakes on his own to lose the bid).
Regardless, if any candidate can keep it close going into super Tuesday this year (02/05/08) they have a chance since
TWENTY states are having their primary that day including two of the monsters (California and New York).