People ask me this question all the time these days.

I have learned to be careful how I answer that question. If my response somehow suggests that either Sen. Clinton or Sen. Obama is not entitled to the nomination, or not yet entitled to it, I may be in for an argument, one that I would just as soon avoid.

Maybe my answer to the "why won't she quit" question will make you angry, too. But since I probably will not be around to hear you shouting if I provoke you, I will give you my best answer.

There are several reasons she keeps on going even though Obama has a seemingly insurmountable lead in convention delegates. Here is the main reason: She is running for president. If it is not to be now, her quest will continue on into a new election cycle.

In the case of this year's nominating contest, Obama may be well-ahead. But this contest has been a close one, and is still close. Until one candidate has a majority of the total delegates, it is not really over. Obama has not yet reached this milestone.

Clinton recently got in trouble for reminding us that in other years the nominating process went well into June. But she was absolutely correct to insist that she had a right to continue to campaign, and, perhaps, an obligation to her supporters not to abandon her effort until the matter is finally settled.

Also, though she certainly made a mistake in alluding to the assassination of Robert Kennedy, it is true that unforeseen circumstances, national or personal to the candidates, could affect the decisions of the unpledged delegates who have the ultimate power to select the Democratic nominee.

Putting aside the outcome of the campaign and assuming that Obama wins the nomination, Clinton's actions are the building blocks for her next, or continuing, quest for the presidency.

If she quits the current contest before every primary is over, she will miss the chance to demonstrate and record for the future the full measure of her voter support. If she does lose this time, she wants it to be very, very close -- as close as she can make it be. Next time, she wants to be able to argue that this year's contest was essentially a tie and that she has earned the right to claim support in 2012 or 2016.

There is something else about next time. She wants to be sure that nobody can ever say that she is quitter. Next time she wants to be able to say, "Support me and there is one thing you can count on. I will never give up, never, never, never give up."

Perhaps Clinton has in mind Ronald Reagan's 1976 losing campaign for the Republican nomination. William Link's recent biography of Jesse Helms, "Righteous Warrior," describes how Reagan's campaign to win the nomination from incumbent President Gerald Ford was floundering until the North Carolina primary. Helms and his allies pulled out the stops to give Reagan a victory in our state, one that gave Reagan the momentum to compete, win primaries and delegates and narrow Ford's lead.

Still, Ford maintained a lead in delegates as the August convention approached, and Reagan was urged to give up.

Instead, he took the battle to the eve of convention with Helms' chief political supporter Tom Ellis using creative tactics to shift delegate support to Reagan.

While the effort to nominate Reagan did not succeed in 1976, his demonstrated strength and fighting spirit helped put him in a position to win the nomination and the election in 1980.

Next time somebody asks me why Clinton does not quit, I think I will just say, "Ronald Reagan," and then turn and run.