Arkansas Sen. Mark Pryor is in the race for his political life against Republican Rep. Tom Cotton. Only you probably wouldn't realize that if you saw him campaigning. (Jeff Simon/The Washington Post)

In private moments, Mark Pryor likes to ask his fellow senators a personal question: What was the thing that got you started in politics?

Some have told him it was the Vietnam War. Others say it was the conservative vision of Ronald Reagan. In most cases, these scarred old pols started out as idealists, with a determination to change something very big in American life.

Pryor himself can’t come up with an answer like that.

“I don’t really have that one issue, or one cause that has gotten me involved in this,” he said. “I just believe in good government, and working hard.”

Pryor (D-Ark.) has been in the Senate for 11 years, holding the seat his father once held for 18. In Washington, Pryor has portrayed himself as a kind of extreme moderate — an almost neutral figure who solves constituents’ problems and helps broker compromises but tries to stay out of big ideological debates.

Freshman Rep. Tom Cotton is challenging Sen. Mark Pryor for his Senate seat in Arkansas. In an interview with The Washington Post, he says the Democratic Party has left Arkansas voters. (Jeff Simon/The Washington Post)

But this year, he can’t be neutral.

Pryor is running for reelection in one of the closest Senate races in the country — and one of the keys to which party controls the Senate. The whole country’s partisan battle could turn on the campaigning ability of this unusual senator, who has spent years telling people that partisan battles are a waste of time.

He’s trying, a little awkwardly, to make it work. On the campaign trail, Pryor is hoping voters would rather have a Democrat with no great crusades than a Republican with the wrong ones.

“I’m really the most independent senator in Washington,” Pryor told a group of about 25 supporters here in the rice-country town of Hazen. “I’m not there to represent the president or his party. I’m not there to oppose the president or his party. . . . My job is to represent Arkansas.” (Pryor noted that he has served under President George W. Bush, a Republican, and President Obama.)

Pryor, 51, is the son of former senator David Pryor (D-Ark.). He grew up in Little Rock, then moved to the Washington area after his father was elected in 1978. Mark Pryor graduated from Walt Whitman High School in suburban Maryland, where football teammates called him “Donny” because he looked a little like teen heartthrob Donny Osmond.

And that might be the single most colorful fact in the entire Mark Pryor biography.

His personality matches his politics: He is low-key and averse to big changes. One of his great pleasures is listening to radio programs recorded long before he was born. “The Maltese Falcon.” “The Shadow.” “He would say things like ‘Listen to the footsteps in the hallway!’ ” longtime aide Michael Teague said, recounting one four-hour car ride, as Pryor was entranced by special effects from more than 60 years ago.

Pryor’s father is a great storyteller, part of a long and entertaining tradition in Arkansas politics. Mark Pryor isn’t. Last week, addressing supporters gathered in a small-town courtroom, the senator looked around and started to say something about his previous career as a lawyer.

“I don’t know if I’ve ever tried a case in this courtroom,” he said. That was it. False alarm. Not a story after all.

But, as bad as Pryor is at lighter moments, he has still touched people in Arkansas with his help in serious ones.

“I want to make sure that you get in there that I’m supporting his opponent, before you say anything nice about him,” said Jeremy Hutchinson (R), an Arkansas state legislator whose father Pryor beat in his first Senate race. He continued: Years ago, Hutchinson’s son was seriously ill, and Pryor — the family’s old rival — called the hospital room out of the blue.

Pryor told Hutchinson about his own bout in the 1990s with cancer, which required surgery to remove muscles from one leg. The two men talked for 30 minutes, dwelling on a terrible thought: “How do you talk about heaven and hell,” Hutchinson recalled, to a child suddenly worried about death?

Hutchinson’s son recovered. He still appreciates the call. “But I will say that he has voted — his voting record, I’m very disappointed in.”

In the Senate, Pryor has voted for key parts of President Obama’s agenda. He backed the economic stimulus package, the Dodd-Frank financial reforms and the health-care law. He also has defied Obama on key issues, including last year’s failed push for tighter gun-control legislation.

But in general, Pryor has tried to portray himself as a figure apart from the everyday political battles. He has helped broker compromises, including a deal that defused a 2005 fight over judicial nominees, and another that allowed for a 2008 overhaul of consumer-product safety regulation.

In his own legislation, how­ever, Pryor usually does not crusade as much as tinker; his efforts most often focus on resolving complaints from Arkansas residents. He changed a Federal Emergency Management Agency rule after the agency surprised families in the state by demanding that they pay back federal disaster aid. He wrote an amendment that changed a Pentagon rule, which had deprived an Arkansas National Guardsman’s family of a payout at his death.

Most senators do this kind of local work and also push for national goals, big changes in what the government spends or who it helps. But Pryor tries to stay away from that kind of big-picture activism.

In an interview, Pryor was asked: What if you suddenly had the power to make Congress do exactly what you want? What’s the first big thing would you want to change?

He said he would use his infinite power to fix . . . the Senate. The process of governing, in other words. Not its outcomes.

“What I would probably change first is just the behavior of senators,” Pryor said. He would make them show more respect for one another, and more respect for the Senate’s time-honored processes.

“You’re not hearing me single out like, this bill, that bill, some other bill, some agenda I have. I mean, I do have bills I want to work on,” he said. “But, even more important, we have to get the process working again.”

This might seem like an odd foundation for a political campaign.

But this year, it has to be.

Pryor is running for reelection against Rep. Tom Cotton (R), a sharply conservative Army veteran with two Harvard degrees. The polls have generally shown that Pryor has at least a slim lead. But Republicans still hope that this will be one of the six seats they need to retake the Senate. That’s because the state has shifted sharply Republican since Pryor took office: In 2012, in fact, Obama lost here by 23 points.

On the campaign trail, Cotton’s main argument is that Pryor isn’t as neutral as he claims. At a stop in Hot Springs, the congressman mentioned the slogan that sits on Pryor’s desk and has served as the centerpiece for Pryor’s Senate campaigns as well as those of his father: “Arkansas comes first.”

“It’s just not true anymore,” Cotton told a crowd of Republican volunteers, reminding them of that vote on the Affordable Care Act. “For five years, he has been putting Barack Obama first.”

Pryor spent last week holding small, low-key meetings with supporters in rural corners of the state. He attacked Cotton for wanting to change big pieces of the federal government, such as the farm bill and Medicare, in the name of cutting back spending. But, where Cotton speaks like a politician — rising and falling and pleading and boasting — Pryor speaks like a minister reading the church announcements.

He didn’t raise his voice, even when he told the crowd, “This is the race of my life.”

In public, Pryor rarely mentions that he’s a Democrat. In private, he is so loath to be identified with his party that he dodged a question about whether — if reelected — he would perform a most basic duty of a Senate Democrat. That would be to support Harry M. Reid (Nev.) to be the majority leader for another term.

“I have not talked to Harry Reid. I don’t know if he’s going to run for leader again,” Pryor said.

Okay, fine, but he’d support some Democrat, right? “Yeah, well. Yeah, maybe,” he said.

Can you really win by being that neutral? If Pryor does, it will because he had help from two important sources.

One is liberal outside groups that have poured money into TV advertising here: $2.27 million already in this campaign cycle (conservative groups have spent more than $4.5 million to help Cotton). For them, the “D” next to Pryor’s name is proof enough that he’s on their side.

The other is the past, and his family’s long history in Arkansas politics. At one recent campaign stop, in Forrest City, Ark., Pryor gave a speech to supporters that barely touched on the fact that he is a Democrat. Afterward, the town’s mayor was asked: How do you know that guy’s really a Democrat at all?

“ ’Cause I knew his daddy,” said Mayor Larry S. Bryant. That was enough.