Can He Be Stopped?

Nagourney lays it on the line:

He now enjoys a big financial advantage. Her big lead in national polls is gone. By most counts, Mr. Obama can now claim more delegates pledged to him. He has won far more states than Mrs. Clinton, although she won some of the big prizes, like California and New Jersey.

She can't win this on technicalities - without pitching the Democrats into a civil war. But does she even know how to concede?