NEW YORK – Pivotal presidential campaigns are frequently defined in retrospect by documentaries.

“The War Room” chronicled Bill Clinton’s political operation in 1992, adding a phrase to the political lexicon in the process. Alexandra Pelosi’s “Journeys With George” captured the oddities of a national campaign on board George W. Bush’s airplane in 2000.

The makers of “By the People: The Election of Barack Obama,” which premieres tonight – Election Night – on HBO, wouldn’t mind the same status.

“That was our hope – that we would create something for history,” said filmmaker Alicia Sams, who made the documentary with colleague Amy Rice and a key assist from actor Edward Norton.

Rice was inspired by Obama’s speech to the Democratic national convention in 2004 and wanted to do a film about him as an up-and-coming political leader. Her friend Sams signed on, but they couldn’t get their phone calls to Obama’s office returned until Norton called on their behalf. He’s still involved as a producer.

They got lucky. They wound up with a far more important story than they had dreamed about.

Even though they began filming nearly a year before Obama announced his candidacy in February 2007, being on the ground early didn’t guarantee them anything. They were nearly shut down when the campaign began.

Obama aides like David Axelrod didn’t want Rice and Sams around. He worried about leaks and whether the presence of cameras would cause people to act like they were in a reality show – concerns that proved amusing in retrospect. Access was a constant concern.

Iowa became their centerpiece. They stuck close to Obama through his early campaigning there, catching moments like a 9-year-old boy making phone calls to drum up support. After three hours of shaking hands, a weary Obama says, “It’s like I’ve been through a wrestling match.”

Through the crowds and contact, the filmmakers sense Obama catching on as he moved toward an impressive victory in the Iowa caucuses. The film introduces audiences to the people around Obama, not just top aides like Axelrod and David Plouffe, but the enthusiastic Ronnie Cho, Obama’s Polk County organizer.

Their discipline and meticulous planning were evident. It was the birthplace of a movement, and whether Obama eventually won or lost the presidency, Rice and Sams felt Iowa gave them a film.

“It was part of the story nobody knew,” Rice said. “When he won Iowa, people started to pay attention.”

Norton said the campaign’s emotional restraint impressed him.

Obama is shown riding in an elevator after having just clinched the Democratic nomination and a film crew member remarks, “You must be feeling pretty good.” The basketball-loving candidate just says, “You don’t cut down the nets for the conference championship.”

“He just seemed so unflappable and what you wondered was, `I wonder if behind the doors it’s like the war room, you know, everybody’s cussing at each other and they’re furious,” Norton said. “When you got round behind the private spaces with them, it was the same.”

Obama saw a rough cut of the film and sent back word that he cried upon seeing the emotional reactions of his staff members to his election.

Cried? Rice doesn’t quite believe that.

That’s what makes extraordinary her footage of an Obama speech the night before the election, after he learned that the grandmother who helped raise him had died a day before seeing the ultimate dream come true. Rice was well-positioned to catch a tear trickling down Obama’s face that night, a view that news cameras penned farther back missed.

On Election Night, Rice shadowed Axelrod and David Plouffe, the aides that once didn’t want her around until she wore them down. She catches the emotional scenes of a headquarters where an implausible dream had come true. She followed the men to an elevator and into Obama’s hotel suite as the campaign architects congratulated the new president-elect.

“Don’t start crying,” Michelle Obama says while hugging Axelrod.

While the film’s release triggers memories of a historic night, it may not be well timed for Obama.

It reaches TV screens less than a month after Obama’s selection for the Nobel Peace Prize, a prize that left many Americans and even the president puzzled about what he had achieved to earn it. Difficult decisions with the war in Afghanistan and health care loom.

The documentary has a laudatory tone; after following Obama for two years, both Rice and Sams said they voted for him. The film could leave Obama fans pining about potential yet unfulfilled and give opponents another example of the media fawning over the president.

“The reaction is going to change on any given day,” Sams said, “and that’s OK. What we want is the movie to stand the test of time.”