William Howard Taft never wanted to be president and yearned instead to serve as chief justice of the United States. But despite his ambivalence about politics, the former federal judge found success in the executive branch as governor of the Philippines and secretary of war, and he won a resounding victory in the presidential election of 1908 as Theodore Roosevelt's handpicked successor.

In this provocative assessment, Jeffrey Rosen reveals Taft's crucial role in shaping how America balances populism against the rule of law. Taft approached each decision as president by asking whether it comported with the Constitution, seeking to put Roosevelt's activist executive orders on firm legal grounds. But unlike Roosevelt, who thought the president could do anything the Constitution didn't forbid, Taft insisted he could do only what the Constitution explicitly allowed. This led to a dramatic breach with Roosevelt in the historic election of 1912.

Nine years later, Taft achieved his lifelong dream when President Warren Harding appointed him chief justice, and during his years on the Court he promoted consensus among the justices and transformed the judiciary into a modern, fully equal branch. Though he had chafed in the White House as a judicial president, he thrived as a presidential chief justice.