Feeling unmoved? Sensing perhaps that you live in uninteresting times? Weary of politicians who define vision as kicking AIDS victims out of the military? If so, historian Stephen Ambrose has a tonic for you.

Undaunted Courage is about a time when America was young, the federal government was bold and the president knew what he was doing. President Thomas Jefferson executed the Louisiana Purchase for a song, doubled the territory of the country overnight and in 1803 dispatched a handsome 30-year-old Virginian to do nothing less than fill in the blanks of our collective future.

Meriwether Lewis, a tobacco grower with an indifferent education, could not remember how to spell his widowed mother's married name. But he could command men, sweet-talk Indians and put a bullet on the mark at a distance of 220 yards. Most important for history, he could, after 12 hours in a canoe, sit down by the campfire and write closely observed and movingly poetic notes about a world that white men had never seen. He explored rivers, mapped mountains and sewed up the West between the Mississippi and the Pacific—and, on his way back home to a hero's welcome in Washington, managed to get himself shot in the butt by one of his own men.

Ambrose, whose 17 previous books include one on D-Day and a highly regarded trilogy on Richard Nixon, showcases himself in this book as an exceptionally shrewd storyteller. In his introduction, Ambrose explains that he and his family have been obsessed with the Lewis and Clark Expedition for 20 years. They have repeatedly followed the explorers’ footsteps across the Great Plains and through the Rockies. That obsession has paid off handsomely. For by digging beneath schoolbook sermons about the expedition, Ambrose has uncovered an extraordinary American character.

Ambrose's Lewis is a tender and tormented soul. Like the West that he conquered, his natural blessings seemed without limit. He was exceptionally good-looking, a kind and loyal friend, an instinctive naturalist and a gifted writer (whose stream-of-consciousness style Ambrose compares to those of Faulkner and Joyce). On meeting the Shoshone, Lewis wrote, “We wer [sic] all carresed [sic] and besmeared with their grease and paint till I was heartily tired of the national hug.”

But he drank too much and he peaked too early.

He was paralyzed after the expedition by what was probably the most significant case of writer's block in this nation's history. The entire world was waiting to read his journals. They would have been a cinch to edit. Yet, for reasons known only to himself, the explorer never turned his journals into a book.

Lewis found it impossible to hold on to greatness. After his grateful friend the president named him governor of the Territory of Louisiana, he did not report to work in St. Louis for nearly two years. He was gamboling in Philadelphia, Ambrose explains, enjoying “too many balls with too many toasts.” When he did take the governor's job, he attempted—and failed—to use his influence to make himself rich. Ambrose believes Lewis was probably a manic-depressive.

In 1809, just three years after his glorious return from the West, his performance as governor came under attack in Washington. While traveling east to explain himself, Lewis surrendered to depression. He was just 35 years old and famous beyond his imagining, and he shot himself in the head. When he did not die, he shot himself in the chest. When he did not die, he cut himself from head to foot with a razor. “I am no coward,” he said as he bled to death, “but I am so strong, [it is] so hard to die.”

With this spectacular young man, then, as the sympathetic heart of his book, Ambrose goes to work as a historian. It's a job he performs with impressive economy and insight. He tells us how Jefferson, “the greatest champion of human rights in American history,” blended paternalism and genocide in his dealings with the Indians. As their “new Father,” Ambrose explains, Jefferson had a nonnegotiable Indian policy—“get out of the way or get killed.”

Ambrose neatly captures the primitiveness of Jefferson's era, a time when no means of transport moved faster than a galloping horse, when the learned president himself believed the Mandan Indians to be a lost tribe of Welshmen, when the cure for the flu was frequent bleeding and massive doses of laxatives.

If this book has a weakness, it's the relative paucity of detail about the Columbia, the great western river that Jefferson had hoped would be the Northwest Passage across the continent. Lewis and Clark disappointed their president by finding that the Columbia did not link up with the Missouri. In seeming sympathy with that disappointment, Ambrose gives short shrift to a river that Lewis and Clark called “inconceivable” and “incredible” and “horrid.” But that, perhaps, is a parochial quibble from a reviewer who was born near the Columbia.

This is a fine and important book, intelligently conceived and splendidly written. It explains how the continental nation was made, flushes out human beings who did the making and reminds us of the magnificent things that government can do when it does have a vision.