Standard caveats aside (it's early, we don't have a set field, blah blah blah), it's hard to see how Mario Cuomo loses the nomination barring scandal or the mother-of-all gaffes.
I've been working up a few scenarios given the primary calendar (which isn't set in stone, with states like California looking to move up), and really, it would be Cuomo's race to lose.
New Hampshire is right next door to Cuomo's New York, and while Dukakis will win it (getting no boost out of it), the race for second-place will determine the "true" winner. Gary Hart, for now, appears to be bypassing Iowa. So the early battle would appear to be between Dick Gephardt and Bruce Babbit. A 2-3 finish for these guys, in any order, leaves them in good shape moving forward.
Nevada will be a battle between Paul Simon Jr. and his union allies, and Al Gore and his suburban base. New Hampshire will be fertile territory for Dukakis and maybe Biden. And then South Carolina. With Iowa out of the big picture thanks to Gephardt, and New Hampshire diluted by Dukakis, South Carolina may well decide our nominee in 2008. Simon thinks he can win the state (I'm not sure how), and he, Gore and Gephardt will stake their entire bids on the state. But given the state's large Italian American population, along with Cuomo's popularity with female voters (yeah, they love him), and it's tough to see how the rest, splitting the dwindling white male vote, can overcome those hurdles.
There's one thing that could put a skid on Cuomo's fast rise -- an Tip O'Neill entrance into the race. Other than that, I don't see a way anyone stops him.