On the campaign trail, Bill Clinton needed the companionship of legions of people, just to talk or play cards through the night. George W. Bush needed his wife, Laura, on board the plane, his feather pillow and plenty of down time.

John F. Kerry just needs to get off the plane.

The protective "bubble" of a presidential campaign is always tedium endured by edgy, ego-driven men who yearn to back-slap and interact. They are confined to the front cabin of a jet for hours on end, hustled from tarmacs into waiting Suburbans and whooshed to underground parking garages. They face crowds they rarely get to meet. The way in which the candidates adjust and cope has long provided a window into their personalities.

For Kerry, independent by nature, the transition from a largely unfettered politician to cloistered nominee has seemed slow and painful, as he tries to find a comfort level both on the road, and in his public persona. His New England reserved, almost laconic demeanor on the trail has worried some Democrats. But his outward demeanor belies a restlessness that has only been exacerbated with the restrictions, according to those close to the presidential candidate.

He has dealt with his rarified confinement by designing his own freedoms and his traveling style -- from a well-utilized cell phone out of the reach of staff, to a virtual traveling gym, to the people he chooses -- or doesn't choose -- to invite on his chartered Boeing 757.

Democrats believe that in choosing as a running mate Sen. John Edwards (N.C.), a man who campaigns with ease and charm, Kerry not only compensated for his own stiffness on the trail but also chose someone who may ultimately help loosen up Kerry. When the two men shared a stage in Miami in April, Kerry hugged Edwards, made jokes and seemed almost giddy. And, as he traveled the country with his new running mate last week, Kerry seemed more energetic than he has in months, smiling widely, toting Edwards's 4-year-old son Jack and making jokes about how their ticket has "better hair" than the opponents. In a joint interview Friday aboard Kerry's campaign plane, Kerry enthused, "We are really having fun."

But this week the double fun ends as the men hit the road separately -- and Kerry must again go it alone.

A zealous athlete and outdoorsman who rides an $8,000 custom Serotta Ottrott bicycle and thinks nothing of wind surfing, Kerry, 60, has found precious little time to stretch his legs. No longer can he wander off solo for a 30-mile bike ride. He has repeatedly asked that time be built into the schedule to allow him to exercise outside -- but the time, aides say, simply evaporates.

Undaunted, he often tries to just steal it back. In Chicago this month, he started to ascend the stairs of his plane after a speech, and then turned on his heels, demanded his football and proceeded to toss the ball with staff -- an increasingly familiar scene for those looking out the windows waiting to depart. "I really need some fresh air," he tells aides on a daily basis.

"It's a very unnatural process because you're being told to limit your exposure when your instincts tell you to get out and see people," said David Morehouse, Kerry's senior traveling aide. "I think it's particularly hard on John Kerry because he's very active."

Aides say that for Kerry, it's not just a matter of carving out an hour at the hotel gym; a stationary bike is delivered to his hotel room at most stops. "He needs to be outside or he needs a vigorous sport," said Michael Meehan, who has worked for Kerry for 18 years. "And on the road it's kind of hard to find 12 men and an ice hockey rink at the last minute."

So Kerry settles for what he can get. Before he boards the plane for every swing, his staff members make sure the required accoutrements are on board: the bicycle (which is toted off and on the plane but barely ridden); his classical guitar (Woody Guthrie's "This Land Is Your Land" is one of his new favorites); three decks of cards (Hearts is his game); and a red, white and blue duffle bag filled with three catcher's mitts, one baseball and one football.

His regular senior traveling entourage includes Morehouse, 43, a veteran of Al Gore's campaign and the Clinton administration who is the effective traveling chief of staff; spokesmen Stephanie Cutter and David Wade; and personal aide Marvin Nicholson, the "body man" who refers to himself as the "chief of stuff." There are also another half-dozen or so staff members who write speeches, give advice or herd the traveling reporters.

Of great curiosity to campaign veterans is that Kerry does not have a "first friend" on board -- a family member or longtime buddy who is his age, has no agenda, can tell him if he's being a jerk and can get staff to back off. Clinton had Bruce Lindsey, an Arkansas friend he had known for decades, and Gore and Wesley K. Clark had their brothers-in-law travel with them.

Kerry's wife, Teresa; his daughters, Vanessa and Alex; and his brother, Cameron, have had sporadic presences on the plane. In addition, various advisers and pols surface, dictated by the issues at hand or geography. Jamie Rubin, a former State Department spokesman, has been on board lately to advise on Iraq; former Clinton Treasury official Roger C. Altman was in San Jose when Kerry was focusing on the economy and technology; and former primary foe Howard Dean held court on the plane when Kerry visited Oregon, where Dean had significant support.

This is just how the Massachusetts senator likes it, say those who know him well. A natural loner, he does not need a traveling friend. "For him it's just not about companionship," one aide said. "It's about intellectual stimulation. It works better for him just to have people rotating on and off, depending on what's going on, to mix it up for him."

Said Tad Devine, a senior adviser, "He's very comfortable. It's not broken."

There is nonetheless a sense that Kerry is not quite comfortable yet -- arduously trying to master the art of campaign discipline while maintaining his sanity.

While never a kidder or particularly engaging with the media as Bush was in 2000, Kerry used to amble to the back of his campaign plane (or bus) and talk with reporters, if for no other reason than to break the monotony of his marathon trips and get a quick political fix on what was happening outside his bubble. Traveling the roads of Iowa during the primaries, he even sang on the bus in front of the media, with his old friend, Peter Yarrow of Peter, Paul and Mary. But that was a long time ago.

Today, Kerry's words are always considered "on the record" on the plane. So, while he is unfailingly gracious, he is more cautious by the day in his interactions. He'll ask reporters what books they are reading, talk about his recent rotator cuff surgery, chat about sports.

He came back for a champagne toast when Associated Press correspondent Nedra Pickler announced her engagement to Peter Haas. Another morning, after reporters and staff enjoyed an evening in New Orleans, he asked one newsman, "What did you do last night? You look green."

Sometimes, the candidate hovers in the doorway of the front cabin to test the waters. A couple of weeks ago, he ventured back to ask for movie recommendations -- and later was seen entering a Boston theater showing "The Terminal,"the flick recommended by the reporters. The other day, he spoke amiably on the tarmac as he tossed a baseball, revealing that he was starting to write out his convention speech longhand.

But he has made it clear he does not want to be pressed. When a reporter benignly asked him over the Fourth of July weekend what he liked about the holiday, he said, "Are you interviewing me?" and moved on.

And if the curious wade into substance, he makes a swift retreat to his small curtained cabin behind the cockpit, not to be seen for days -- relying on his cell phone, the many aides who fill his needs and his fleeting contact with real people on the ground.

Largely gone are the long, verbose speeches, for which he was widely criticized. Today, he sticks with the text. But still missing is consistent passion. One day he can bring a union audience to its feet repeatedly with cries for economic equity. The next he'll deliver the same speech with no emotion and little tempo, turning it into a rote stump speech.

He seems to charge his batteries with voter contact. Once, he jumped a barricade to shake hands. He works a crowd for as long as it takes or as long as his schedule will permit. At a Detroit restaurant recently, he shook hands with every patron (some twice) and kitchen worker, then started autographing T-shirts on people's backs. In New Orleans, he spotted a wedding party across the street from his hotel and made a beeline. Before the startled bride knew what was happening, Kerry was standing on the step of her horse-and-buggy.

He truly seemed to be enjoying himself in December and January when the campaign was struggling to survive and he let loose. Aides say they are starting to see some of that come back. About 1 a.m., during a recent cross-county flight, Kerry broke from his game of Hearts with staffers to lead a prank on Rubin.

As Rubin slept, curled up in a chair, Kerry placed next to him "Pepe the Pinata," a large, multicolored papier-mache dog, and covered them both with a blanket. He summoned the staff photographer and staged a photo that looked like Rubin was cuddling with the dog.

Another day, Kerry was positively ecstatic when the flight attendants sang a song one of them wrote. To the tune of "Proud Mary," they crooned "Proud Kerry." He hugged and kissed all of them when it was over.

An avid reader, Kerry usually has a half dozen books going at once on the plane. Most recently he has been reading "The Two-Income Trap: Why Middle-Class Mothers and Fathers Are Going Broke," Walter Isaacson's "Benjamin Franklin: An American Life," David Halberstam's "The Teammates: A Portrait of a Friendship" and Robert Caro's "Master of the Senate."

He prefers actual newspapers to a prepared clipping book and will read three or four newspapers a day, quizzing aides relentlessly about certain articles that catch his eye. He will also tinker with his speeches for hours, up until the minute he delivers them. "Not necessarily for substance but to make sure it sounds right to the ear," Rubin said.

In addition, aides say, he entertains himself with movies on cross-country flights or late at night in his hotel room. He watched "The Godfather" and "Animal House" on some recent long flights.

"I'm usually the last one around at night," said Nicholson, the body aide. "The other night we watched 'Seabiscuit.' Again."

Staff writers Dan Balz, Jonathan Finer and Dale Russakoff and researcher Lucy Shackelford contributed to this report.

Sen. John F. Kerry, left, and spokesman David Wade on his campaign plane with reporters, with whom the candidate has grown more cautious.