For the sake of that 5 percent, this will be the sourest spring. About a fifth of Clinton and Obama supporters now say they wouldn’t vote for the other candidate in the general election. Meanwhile, on the other side, voters get an unobstructed view of the Republican nominee. John McCain’s approval ratings have soared 11 points. He is now viewed positively by 67 percent of Americans. A month ago, McCain was losing to Obama among independents by double digits in a general election matchup. Now McCain has a lead among this group.

For three more months, Clinton is likely to hurt Obama even more against McCain, without hurting him against herself. And all this is happening so she can preserve that 5 percent chance.

When you step back and think about it, she is amazing. She possesses the audacity of hopelessness.

Why does she go on like this? Does Clinton privately believe that Obama is so incompetent that only she can deliver the policies they both support? Is she simply selfish, and willing to put her party through agony for the sake of her slender chance? Are leading Democrats so narcissistic that they would create bitter stagnation even if they were granted one-party rule?

The better answer is that Clinton’s long rear-guard action is the logical extension of her relentlessly political life.

For nearly 20 years, she has been encased in the apparatus of political celebrity. Look at her schedule as first lady and ever since. Think of the thousands of staged events, the tens of thousands of times she has pretended to be delighted to see someone she doesn’t know, the hundreds of thousands times she has recited empty clichés and exhortatory banalities, the millions of photos she has posed for in which she is supposed to appear empathetic or tough, the billions of politically opportune half-truths that have bounced around her head.

No wonder the Clinton campaign feels impersonal. It’s like a machine for the production of politics. It plows ahead from event to event following its own iron logic. The only question is whether Clinton herself can step outside the apparatus long enough to turn it off and withdraw voluntarily or whether she will force the rest of her party to intervene and jam the gears.

If she does the former, she would surprise everybody with a display of self-sacrifice. Her campaign would cruise along at a lower register until North Carolina, then use that as an occasion to withdraw. If she does not, she would soldier on doggedly, taking down as many allies as necessary.