WHAT IT TAKES: The Way to the White House, by Richard Ben Cramer, Random House, 1,047 pages, $28.

If one were to poll, say, a fifth-grade class, many would say they one day would like to become president of the United States. But just what is it that propels a person to actually follow that grueling path decades later?

In “What it Takes: The Way to the White House,” Pulitzer Prize winning journalist Richard Ben Cramer tailed four Democrats and two Republicans as they started that perilous journey in 1988.

The first words of the book, in the author’s note, illustrate Cramer’s thesis: “None of my friends ever thought he should be president — much less that he could be. … A president — the president — was someone altogether larger, and more extraordinary, than we.”

Earning the Oval Office is, of course, more than just making speeches and collecting 270 Electoral College votes. Serious candidates will soon discover that they must immerse themselves in “the bubble,” sacrificing their time, their privacy, their family, and, in a sense, part of their identity.

Cramer began his quest with two questions: “Who are these guys? What are they like?”

Cramer is the fabled fly on the wall, bringing the reader into the candidate’s head, tracing his history down to the smallest detail, and providing a gestalt of the people voters usually saw as long-winded talking heads four years ago.

We are there when young Michael Dukakis is told by his teacher to bring a note from home explaining why he was late for school: his mother replied that Mike shouldn’t have been late, that there was no excuse for it.

We are there when Bob Dole, under German fire during World War II, is shot by the enemy, loses the use of his arm, and then fights day after day, year after year, to make himself as whole as possible.

We are there when George Bush declines the post-Pearl Harbor advice of Secretary of War Henry Stimson to go to college, opting instead to enlist in the Navy on his 18th birthday.

And we are there as Lee Hart is besieged by reporters as husband Gary fends off reports of womanizing and withdraws from the race.

Years from now, “What it Takes” is likely to stand near the top, if not at the crest itself, of the mountain of presidential-race books. It is a magical book, written in quick-moving prose that gets beyond the sound bite to show that these six men differed on politics, but essentially were of the same fabric.

They were overachievers, they all suffered devastating personal tragedy, they were basically good people, and, most of all, they believed they would be president.

John Ripley is a reporter on the NEWS Government and Politics Desk.