This gap will only get bigger as Christie's post-Sandy popularity fades and Democrats "come home" to Hillary. Also, Christie will be pushed toward the right if he wants to win a Republican primary, so that will not bode well in liberal New Jersey. I think Christie will definitely keep it in single digits against Clinton, but he'd likely lose by 8 or 9 rather than 5 given that it is 2013, and the election is three years away. He could probably beat some of the weaker Democrats, or definitely at least bring it into a 3-4 point margin.
Do you have any evidence to back this up? I mean, this whole paragraph just sounds like a wishful pipe dream.
Also, you didn't even mention Hillary's primary. Did you mention she could destroy here chance at winning the "Clinton but not Obama" states by going too far left in the primary? Or do democrats never go to far left? And yes, Christie will be forced to move farther right in his primaries and his strength in New England will probably fade as well.
When Dennis Kucinich ran for president in 2004 and 2008, he was pretty much ignored and never polled more than 1%. He didn't drag anyone to the left. Compare to fringe figures on the right like Bachmann, Cain, etc. who ended up dragging Romney to the right because they were once leading him in the polls.
A good example on the left would've been if Kucinich's presence forced every Dem candidate to commit to ending the Iraq War on their first day in office and then prosecuting the Bush administration for war crimes. Obviously didn't even come close to happening.