The next president shouldn't strive for greatness, which would confer historical reputation but require more than the rest of us can bear. Being a good president will be good enough.

H. W. Brands' new book is "The Man Who Saved the Union: Ulysses Grant in War and Peace."

Joan Hoff: Presidents and war

A review of polls of presidential scholars since 1948, but especially since 1962, reveals that all of the top great or near-great presidents, except for Thomas Jefferson and Theodore Roosevelt, were involved in war during their presidencies. Six of them -- James Polk, Lincoln, Woodrow Wilson, FDR, Truman, and Dwight D. Eisenhower -- were wartime presidents. LBJ, Richard Nixon, George H. W. Bush, and George W. Bush have not secured great or near-great status in these polls because of the failed Vietnam War, the successful but forgotten First Gulf War, and the misguided invasion of Iraq based on false intelligence.

Given the length, expense and unpopularity of the wars in Iraq and Afghanistan, it is conceivable that future presidents may not automatically receive the vaunted accolade of presidential greatness when they commit the nation to military action.

Taking action in a time of perceived crisis is also not always wise, as demonstrated by JFK's Bay of Pigs fiasco, Jimmy Carter's mishandling of the U.S. hostage situation in Iran, and Reagan's hostage-for-arms scandal known as the Iran-Contra affair.

This leaves us with the greatness of Jefferson and Theodore Roosevelt. How did their success as leaders emerge without waging war? Importantly, both were intellectuals while most of the wartime presidents were not. So their writings and peaceful actions enhanced their reputations as thoughtful presidents. Despite Jefferson's silence about his own slaves, the principles of the Declaration of Independence about fundamental human rights and equality still ring true. He also doubled and explored the nation's land area and established the precedent of executive privilege.

Likewise, Roosevelt -- despite his macho association with the Rough Riders during the Spanish-American War and his great white hunter lifestyle -- was the first president extensively to preserve national forests and parks, support civil service reform, oppose unregulated great corporations, and promote inspection of food and drugs. He also was the first American president to win the Nobel Peace Prize, because of his mediation of the Russo-Japanese War.

Responding to crises and initiating wars may not represent the best way to determine the greatness of American presidents for the rest of the 21st century.

Joan Hoff, author of "Faustian Foreign Policy from Woodrow Wilson to George W. Bush," is research professor of history at Montana State University.

Joseph Ellis: When major crisis strikes

Presidential greatness is a rare thing.

The three greatest American presidents -- George Washington, Abraham Lincoln and Franklin Roosevelt -- all came to office at times of great crisis. Washington created a nation out of a confederation of states. Lincoln saved the nation that Washington created from dissolution. Roosevelt rescued the capitalistic economy of the nation from the Great Depression and, in World War II, its democratic legacy from totalitarianism.

If history is a guide, then, presidential greatness only occurs in the crucible of major crises. If Islamic terrorists detonated a nuclear bomb in New York or Washington, or if an American attack on Iran's nuclear facilities generated a widespread war in the Middle East, then the conditions would exist for the display of presidential greatness.

Let's hope that neither Barack Obama nor Mitt Romney will have to face such a predicament.

Joseph J. Ellis is the author of the Pulitzer Prize-winning "Founding Brothers: The Revolutionary Generation."