It is common ground among historians that the presidency has grown and accumulated powers. At the founding, some people expected the presidency to be a ministerial office that would simply put into effect policy chosen by Congress.

George Washington had different ideas, however, and helped set precedents that future presidents would take advantage of. Through most of the 19th century, there were some powerful presidents (notably the early Virginia Dynasty presidents, Jackson, Polk, and Lincoln) but most were junior partners with Congress.

All of this changed in the 20th century. Starting with Theodore Roosevelt, presidents increasingly asserted their right to make and execute policy, especially in the area of foreign affairs and during times of crisis. Franklin Delano Roosevelt enjoyed quasi-dictatorial authority over both the economy during the Great Depression and foreign relations during World War II.

The second half of the 20th century saw the institutionalization of the massive powers claimed by strong presidents like FDR, Theodore Roosevelt, and Lincoln. The budget and staff of the executive branch exploded. For the first time, the United States would have an enormous army permanently stationed around the world during peacetime, and it fell to the president to lead it.

Meanwhile, the national government took over the regulatory powers that had been exercised by the states. The massive national regulatory apparatus was lodged in the executive branch and was thus, too, put under control of the president.

Congress and the judiciary became increasingly marginal institutions. Congress delegated much of its lawmaking powers to regulatory agencies under the thumb of the president. Courts, too, lost their common law regulatory powers to these agencies. Congress and the courts could react to presidential power in various ways — slowing down projects they disapproved of, adjusting them along the edges — but they could not set policy or block the president’s agenda.

To be sure, both institutions retained the formal power to constrain the president. But Congress is a creature of politics, so as people increasingly turned to the president to solve their problems, Congress was forced to go along with the president’s agenda.

President Bush went to Congress for counterterrorism authority, but Congress could not deprive him of what he wanted. He, not Congress, set the policy. President Obama has gone to Congress for his financial regulation and health care laws; again, Congress could not say no to him. And both laws simply give the president various blank checks to regulate.

For most commentators, these trends are matters of significant disquiet. Under the founding design, Congress, not the president, is supposed to make policy; and courts are supposed to enforce the laws that incorporate that policy. The academic effort to reinvigorate the archaic system of checks and balances is fundamentally nostalgic and reactionary. These institutions are as out of place today as the cocked hats and breeches worn by the founders as they drafted the Constitution.

What has changed? Eighteenth century America was lightly populated, rural, agricultural, and (among the elites who counted) homogenous. Customs and honor counted a lot more for regulation than formal legal institutions did. Dangerous foreign enemies were at a safe distance. Life moved to the slow rhythms of the country lane.

Today, America is huge, diverse, and commercial. Foreign relations are a constant series of crises that must be managed hour-to-hour. The domestic economy is enormously complex, ever-changing, and interconnected. Only one institution can realistically handle these 21st-century challenges, and that is the executive. The presidency has blossomed because Congress, the courts, and the state governments could not handle these challenges as they emerged in the last century.

The major political challenge today is keeping the executive within bounds. But it is no longer possible to rely on Congress and the judiciary to do that. The party system, the media, a communications revolution that has kept the citizenry informed and politically engaged — these institutions are infinitely more important.