Barack Obama is in a slump, with a few pedestrian interviews, a behind-the-curve economic speech and some miscues. Expectations for his inaugural address on Tuesday are in the stratosphere.

This is just what he relishes, pressure to perform.

The world may well see not only a remarkably historic moment on the west front of the US Capitol but also one of a handful of truly memorable inaugural speeches.

Inaugurals are unique, defining moments for a president. They are neither the time for a laundry list of policy prescriptions nor partisan moments. They are opportunities to galvanise the nation around the central themes and issues of the day.

That's why most of the memorable addresses have been in times of crisis — Abraham Lincoln during the Civil War and Franklin D. Roosevelt during the Great Depression. Two of the rare exceptions were John F. Kennedy and Ronald Reagan, carried by the magic of their words capturing the essence of their times.

After Obama takes the oath of office, on Lincoln's Bible, he will be talking to a global audience that knows these aren't normal times, not the magnitude of crises that Lincoln and FDR faced, but greater than those which Kennedy or Reagan confronted.

"This is an occasion that calls not just for soaring inspirational words," says Ross Baker, a political scientist at Rutgers University in New Brunswick, New Jersey, who has studied inaugural addresses. "It is not a time for pious reassurances. But he has to appeal to Americans about the enormous costs that have been exacted upon us and the challenges for the times ahead."

To the rest of the world, he must show both a sense of strength and of a less-belligerent posture for the US

To his fellow citizens, he needs to convey a confidence and a sense of the sacrifices and possibilities that lie ahead.

Obama is one of the most gifted of orators. He manages to be persuasive, even passionate, without being shrill. He combines the cadence of the old civil rights preachers with the elegance of JFK.

"Obama brings a rare combination," says David Eisenhower, a professor at the University of Pennsylvania who teaches courses on political rhetoric. "He is able to appeal intellectually and also to inspire."

After a spectacular first two months, Obama's presidential transition hit some speed bumps this past week. Some politicians suggest some of the lustre is wearing off before he assumes office.

That's reminiscent of last March when he lost key primaries to Hillary Clinton, was fumbling on the campaign trail and got hit with the controversy over incendiary remarks by his pastor, the Reverend Jeremiah Wright. This led to the speech in Philadelphia that he gave on race.

"That was maybe the greatest speech by a contemporary American politician," Baker says.

Another candidate for that distinction is Kennedy's 1961 inaugural address. It was the height of the Cold War, but not a time of unusual peril. Kennedy captivated a nation with soaring rhetoric — "Ask not what your country can do for you, ask what you can do for your country." The young president brilliantly framed the generational change in declaring, "the torch has been passed to a new generation of Americans."

In a style not dissimilar to Kennedy's, Reagan 20 years later set the tone for his administration: "Government is not the solution to our problem."

A century earlier, Lincoln, in a different context, was grandiose and conciliatory in his inaugural addresses. In the first, desperately trying to preserve the Union and avoid civil war, he vowed not to "interfere with the institution of slavery in states where it exists. I believe I have no lawful right to do so, and I have no inclination to do so."

Four years later, after the bloodiest war on American soil, with 620,000 dead, he responded to the vanquished with a final thought that is unsurpassed in American political rhetoric: "With malice toward none, with charity for all, with firmness in the right as God gives us to see the right, let us strive on to finish the work we are in, to bind up the nation's wounds, to care for him who shall have borne the battle for his widow and his orphan, to do all which may achieve and cherish a just and lasting peace among ourselves and with all nations."

The moral strength that an inaugural speech can command in tough times also was exemplified by Roosevelt. In March 1933, America, ravaged anew by the Depression and a loss of its can-do spirit, heard the new president declare: "The only thing we have to fear is fear itself."

In 1937, while the economic hard times persisted, the second FDR inaugural address reflected the resolve that "democratic government has the innate capacity to protect its people against disasters once considered inevitable, to solve problems once considered unsolvable."

He spoke of seeing "one-third of a nation ill-housed, ill-clad, ill-nourished," and expressed determination that would be changed: "The test of our progress is not whether we add more to the abundance of those that have much; it is whether we provide enough for those who have too little."

Obama may not rise to the Lincoln and FDR levels. The news Web site Politico quoted one aide as saying he will try to be "soaring but accessible, simple but inspiring, urgent but confident." That would be worthy of the moment, the inauguration of America's first African-American president.

Providing, that is, he appreciates the importance of brevity. In 1841, President William Henry Harrison gave the longest inaugural address — two hours, 8,500 words — in freezing weather.

Thirty days later, Harrison died of pneumonia.

n Albert R. Hunt is the executive editor for Washington at Bloomberg News. The opinions expressed are his own.