James A. Johnson is a quiet, serious sort, much given to sober gray suits and conservative rep ties, proud of his own reputation as a man of probity and unassailable integrity. He’s the son of a Minnesota politician but more comfortable just out of sight.

Now, however, he’s at the center of the political universe, and very much in the sights of the political class. The Democratic presidential campaign is over, all but the shouting, of course, and the focus has moved on, turning from the nomination battle to the selection of the running mate for Sen. John F. Kerry of Massachusetts. It is the obsession of people who think, wrongly most of the time, that this makes much of a difference. It doesn’t, and hasn’t since Lyndon B. Johnson helped John F. Kennedy take Texas.

No matter. Jim Johnson now has a job to do — help Kerry choose the bottom of the Democratic ticket — and he’s going to do it. One thing you can bet is that he’s going to do it thoroughly. Just this weekend, for example, he was reading Clark Clifford’s account of the LBJ selection and going over the notes of the late Phil Graham, the Washington Post publisher who played an important role in 1960. Last week he had a long talk with Warren Christopher, the former secretary of state who helped Bill Clinton choose Al Gore and, Gore being pleased with the way the selection worked in 1992, helped Gore choose Joseph I. Lieberman in 2000.

“This job is easier this time than in 1992,” said Vernon L. Jordan, the Washington lawyer who was involved in the Gore selection in 1992, “because this time there won’t be anyone who doesn’t think the Democrats can win.”

Even so, this is one of the most unusual job searches in America, and part of it is to appear open to all constituencies and all voices. This is a Johnson specialty. No one, except maybe his son Alfred, ever recalls Johnson, 60 years old, saying no to anyone. He doesn’t always say yes, but never no. It is the key to his success.

This is serious business, and if you don’t think so, perhaps the names Theodore Roosevelt, Calvin Coolidge, Harry S. Truman and Lyndon Johnson will make the case. Overall America has been lucky in its vice presidents, at least after Andrew Johnson, and though Mark Hanna is remembered for lamenting when TR succeeded William McKinley that “that damn cowboy is president now,” the men who have stepped into the Oval Office have been sound and, in some cases, exceptional. That’s at the heart of Johnson’s worry. “The overwhelmingly most important criterion,” he said in a conversation Sunday, “is that the person selected is clearly qualified to be president of the United States.”

He’ll get loads of advice, most of it worth what it cost, almost all of it unsolicited, a good deal of it boosting Sen. John Edwards of North Carolina.

There’s a good reason for that — the widespread view that, as Democratic consultant James Carville put it the other evening, “you don’t leave your best horse in the stable.”

But it’s not simply a question of horses, or of breeding. Kenneth B. Mehlman, the campaign manager for President Bush, believes vice-presidential selections are subtle ways to make an important statement. The choice of Richard B. Cheney, for example, helped the GOP convey the notion that Bush was serious about governing. The selection of Gore gave a youthful, forward-looking air to the Clinton campaign. The selection of President Bush’s father in 1980 helped persuade some voters that Ronald Reagan was more than a Western gunslinger. And the choice of Lieberman four years ago allowed Gore to make a subtle declaration of independence from Clinton, particularly on moral questions.

“If you choose the right kind of vice president, it can reinforce something about you that you want the public to understand,” Mehlman says. “If I’m Kerry, I’d think about what leadership attribute I’d like the public to visualize.”

Ahh, so this is not so easy after all.

Johnson has been through this one time before. Two decades ago he was the campaign manager for former Vice President Walter F. Mondale. The selection of Rep. Geraldine A. Ferraro of New York provided an important moment for the Mondale campaign; when Mondale announced the historic selection of a woman for the national ticket, a tear formed in the eyes of a stolid state trooper in the state capitol building in St. Paul. The San Francisco convention was electrified. Even so, Mondale lost 49 states, and questions about the finances of Ferraro’s husband provided a costly distraction to the campaign.

But the 1984 experience remains an important one in Johnson’s mind; it’s central to his experience. The selection process in 1984 was run by John R. Reilly, a one-time Robert F. Kennedy aide who had the complete trust of the candidate.

“I had an advantage,” Reilly recalled this week. “We were on the road together. Mondale and I were friends. We had dinner together — alone — once a week. We’d talk about what he’d want in a vice president — someone to help on the Hill maybe, someone perhaps to help with foreign affairs. I think Jim can probe and get that kind of information out of Kerry.”

That’s the task Johnson has. Right now he has no schedule, no short list. This week he’ll begin to make the rounds on Capitol Hill, consulting with party leaders. “At the early stage of this process, we’re soliciting the views of the broadest possible group of people,” he says. That’s the early stage. At the end it won’t be primarily Johnson’s choice. It will be the first important, and perhaps most enduring, choice the Democratic nominee for president will make.

David Shribman is a columnist for Universal Press Syndicate.