Is there a second-term curse on presidents? It's widely believed that the answer is yes. Look at Richard Nixon: re-elected with 61% of the vote in 1972, forced to resign under threat of impeachment. Ronald Reagan: re-elected in 1984, then hobbled by the Iran-Contra scandal two years later. Bill Clinton: re-elected in 1996 promising to build a bridge to the 21st century, then impeached by the House of Representatives for lying under oath. George W. Bush: re-elected in 2004, only to see his job-approval rating plummet amid scenes of violence in the streets of New Orleans and Baghdad in 2005 and a financial crisis in fall 2008.

There is a classic explanation for this supposed curse, summed up in a single word: hubris. The re-elected president overestimates his mandate. He ignores opposition and pursues goals that prove to be beyond reach. Freed of the need to seek re-election, isolated by the perquisites of office, he plunges ahead—only to fall off a cliff.

There is something to this. But when you look beneath the list of second-term disasters, you also find some significant successes. It isn't a long list, though: Barack Obama is only the 16th president to have been elected to two consecutive terms.

Two presidents, Abraham Lincoln and William McKinley, were assassinated in the first year of their second term. But both were arguably successful in the short time they served. Lincoln began the 41 days of his second term by delivering his Second Inaugural, the most sublime presidential speech in our history, and then saw Lee surrender to Grant.

McKinley achieved victory in the Spanish-American War, acquired Hawaii, Puerto Rico and the Philippines and maintained the gold standard, laying the basis for a long period of prosperity and innovation.

Five re-elected presidents were confronted with challenges raised by major European wars. George Washington faced a world war between revolutionary France and royal Britain in which large numbers of his fellow citizens sympathized with both sides. He is probably the only man who could have held the infant republic together in this crisis. Thomas Jefferson, faced with world war between Britain and Napoleonic France, stumbled when he ended foreign trade with the 1807 Embargo. His chosen successor, James Madison, started the War of 1812 and saw the Capitol and the White House burned down in his second term.

Woodrow Wilson, after narrowly winning re-election in 1916 as the president who "kept us out of war," led the U.S. into World War I shortly into his second term. His suppression of civil liberties and crusades against German culture stoked resentment, and his stubborn refusal to accept reservations to the Versailles Treaty made him vastly unpopular. In his last two years he lay sick in the White House as the nation was beset by inflation, recession and terrorist bombings. His party's presidential nominee was defeated by the largest percentage margin in history in 1920.

The next Democratic president, Franklin Roosevelt, had a dismal second term, as the nation stayed stuck in depression. When World War II broke out in 1939, most Americans were determined to stay out. But after the fall of France in June 1940, Roosevelt set about aiding the British in their lonely fight against Hitler. He built up the military, got Congress to authorize the draft and set businessmen like William Knudsen and Henry Kaiser to assemble what would be known as the arsenal of democracy. He was rewarded with a third term in 1940 and, after a brilliant performance in setting strategy and choosing military commanders, a fourth in 1944.

Four other presidents had mostly successful second terms. James Monroe produced the Monroe Doctrine in 1823. Andrew Jackson won his fight against the Bank of the United States, and on his last day in office he recognized the independence of the Republic of Texas, which led to its annexation eight years later. Ulysses S. Grant, reviled for years by historians, failed in his Reconstruction efforts to uphold the rights of Southern blacks. But he succeeded in pushing the U.S. toward the gold standard. And Dwight Eisenhower, despite the condescension of the liberals of his time, is now conceded to have done just fine.

To that list could be added Theodore Roosevelt and Calvin Coolidge, who could have been re-elected in 1908 and 1928 had they chosen to run. TR regretted his decision, ran again in 1912 and lost, but he was the favorite for the 1920 contest when he died suddenly in January 1919. Less successful were Grover Cleveland, who endured a recession in his second, nonconsecutive term; Harry Truman, whose domestic agenda was rejected and who was unable to break the stalemate in Korea; and Lyndon Johnson, who lost heart once we seemed mired in Vietnam.

In retrospect, second-term problems resulted more often from the failure to adjust to changed circumstances and unanticipated challenges than from the hubristic pursuit of first-term goals. This can even be said of Nixon, who complained with some justice that sins of his predecessors as egregious as Watergate had been overlooked.

As for Reagan and Clinton, despite Iran-Contra and impeachment, their second terms were mostly policy successes. Reagan got tax reform and an arms agreement with Russia even while urging Mikhail Gorbachev to tear down the Berlin Wall. Clinton got a balanced budget and a capital-gains tax cut. Both maintained job approval at 50% or more in times of apparent peace and prosperity.

The same cannot be said of George W. Bush. His 51% re-election percentage didn't provide the political capital that he needed to reform Social Security, and his surge strategy in Iraq came too late to elevate his job rating. We will see how much political capital Mr. Obama's gets from his 51% re-election percentage—down from 53% in 2008. He is the first president since Wilson to win a second term with a reduced percentage margin.

The second-term curse isn't inevitable. But the only sure way to avoid it is to follow the precedent of James K. Polk and Rutherford B. Hayes, who kept their early pledges not to seek re-election.