Clearly, there is much to be said for determination, and Senator Clinton is to be admired for her staying power. There is no doubt, too, that Hillary Clinton will make a fine president, and a far superior one to the one we have at present, or anything her opposing party can offer.
That said, public service, by definition, means putting the needs of one's country above one's own, so if there is only a 15% chance that extending the primary season may contribute to a defeat in November, the right thing to do would be to walk away.
History shows that courage doesn't mean standing on principle, but taking a principled stand.
The right thing is seldom the easiest, and often the least personally gratifying. But, if Senator Clinton means what she says about changing the direction of this country, and infusing the body politic with integrity, countering the damage to our national reputation of the past seven years, then she must lead by example, and show that, unlike our current commander-in-chief, she is listening not to her own voice, but to the voice of the American people.