Theodore Roosevelt didn’t plan to become president. In 1901, after President William McKinley was assassinated, the 42-year-old vice president was sworn in—becoming the youngest person ever to occupy the White House. Many in the Republican Party had hoped to sideline Roosevelt’s reformist energy by placing him in a quiet, symbolic role. But Roosevelt had other ideas. He brought his convictions...

We Americans have many grave problems to solve, many threatening evils to fight, and many deeds to do, if, as we hope and believe, we have the wisdom, the strength, the courage, and the virtue to do them. But we must face facts as they are. We must neither surrender ourselves to foolish optimism, nor succumb to timid and ignoble...