Can the Democratic Nomination be won?

A commenter, Andy, challenges the possibility that the Democratic race might end before the Spring is over:

If it goes past March 4, I don’t see how PA or anything else would solve it. And frankly, I’m not sure anything will solve it. Do the math. I think there are about 1,400 pledged delegates left. They both need close to 1,100 to get the nomination. Barring something really unexpected, neither is going to come close to winning that many of the remaining delegates when it’s still even. That would mean it’d come down to superdelegates at the convention, unless one of them gives up for the sake of party unity.

I can think of two ways for the race to wrap up earlier. There might be more.

Hillary scenario. They trade narrow victories, Hillary maintains a narrow edge (or slightly expands it).  Economy does not tank and Iraq does not fall apart, and a McCain victory in November seems more possible. Key superdelegates push for party unity, and major supporters of both sides decide, facing deadlock, that Hillary has earned the shot, and pressure Obama to withdraw.

Obama scenario. He has a cash edge, is fundraising stronger, and now with 1 – 3 states at a time, can win almost every race. He really could, starting with Louisiana, Nebraska and Washington tomorrow. Maine is Sunday. Maryland, Virginia and DC are Tuesday. Obama is leading in the three on Tuesday, and could well have wins or draws in the others. The next week: Wisconsin and Hawaii. Again, could well go to Obama. That leaves Hillary’s firewall on March 4 in Rhode Island, Vermont, Ohio, and Texas. If Obama goes in with momentum, he could draw, and Hillary could give up the ghost.

The delegate math says that one of them needs to win two to one the rest of the way, which is not impossible, but not likely. But there are scenarios that let this end in Pennsylvania.