On March 21, Obama reached his Portland, Ore., hotel around midnight, after a cross-country flight from West Virginia. A few hours later, he was up greeting New Mexico Gov. Bill Richardson, who would endorse him at a morning rally in Portland. After a morning news conference, a town hall meeting in Salem and a boisterous stop in Corvallis, Obama rolled into Eugene for a 9 p.m. rally at the University of Oregon. Not done yet, he boarded his plane and landed in Medford well past 1 a.m.

For the Clinton camp, the fatigue is compounded by the drumbeat of pundits and opponents declaring her campaign dead or calling on her to drop out. Sean Johnson -- a political aide with a wife, a 6-year-old daughter, Sydney, and a 5-year-old son, Carter, in White Plains, Md. -- joined up in early 2007 and began his life as a road warrior three months ago. The buildup to the Maryland primary was considerable, and Johnson was working on the home front. His wife, Rhya Marohn, a house-calling veterinarian, was running as a Clinton delegate.

Then Clinton got trounced in the Potomac Primary. When Sydney asked her father how his boss had done, he had to be honest.

"Well," the girl chirped, "we just have to go win Texas," and three days later, Johnson was off to the Lone Star State.

Usually, long before spring, primary campaign staffs are rejuvenated with new blood from other campaigns that have gone under. Jobs and roles change to keep people from languishing. The Clinton team has gotten some fresh legs. Under duress, the candidate brought in a new campaign manager, Maggie Williams, in February, then a new pollster, Geoff Garin, who became a strategist this month.

But the tight-knit Obama camp has remained small, stable and overworked. Last year, Democratic campaign veteran Steve Hildebrand turned down a top job with the campaign, not wanting to leave his home and business in South Dakota. He finally joined, with the understanding that he would handle the first four states and that was all.

Instead, he has become the deputy campaign manager. Those four states turned to 44, and he is now in the Chicago headquarters he had hoped to avoid.

Obama jokes to crowds that in the 15 months since he launched his campaign, "babies have been born and are now walking and talking."

But for the candidate and his staff, the grind has been no joke. Most Obama staffers signed up at the beginning of the race, with no expectation that when May rolled around, the battle would still be raging. But they are still sitting in hotel lobbies at 1 a.m., typing up the next day's schedule or working out logistical glitches.

Robert Gibbs, Obama's communications director, sees his young son so rarely that he brought the boy to Dulles International Airport one recent morning so they could spend time together before the plane took off. Campaign manager David Plouffe moved his family to Chicago, but although he lives a short walk from downtown headquarters, he is hardly ever home. Last weekend, Jewish staffers borrowed a conference room at the Harrisburg, Pa., Sheraton to hold a Passover seder.

Adding to the strain is the race's shifting momentum, along with the false hope raised at several intervals that an end would be just around the corner. Obama's losses in Texas and Ohio dealt a serious psychological blow to his staff. They had counted on a better outcome -- if not nudging Clinton out of the race, then at least easing the pressure until the Pennsylvania primary six weeks later. Many had already made vacation plans. But their traditional sojourns to spring training became a three-day Easter weekend, overlapping with Obama's family trip to the Virgin Islands.

The candidate tries to swing through Chicago about once a week, sometimes for just a few hours. The night of the Pennsylvania primary, Obama flew from Philadelphia to Evansville, Ind., held a 10 p.m. rally, then headed back to the airport to fly to Chicago. He got home after 1 a.m. and was back at Midway Airport by 8 a.m. to return to southern Indiana for another event. Obama was notably flat at the New Albany town hall, but he did get to have breakfast with his daughters.

Bill Burton, Obama's press secretary, was one of the first four people to sign up with the campaign. On July 7, he took time off to get married. Since taking his vows, he has gotten Christmas and Thanksgiving off and one three-day weekend with his wife and their dog in St. Michaels, on Maryland's Eastern Shore.

"I think my wife has been a real hero on this campaign," he said. "When you sign up to marry a guy, you don't expect that you're not going to see him for more than a year."