Washington ? Four years ago when the newly inaugurated President George W. Bush called on his fellow Americans to “show courage in a time of blessing,” he could not imagine the horrors of the Sept. 11 terrorist attacks or the demands of war in Afghanistan and Iraq.

On this day of his second inauguration, the only certainty is that the next four years will present challenges as large and unexpected as those of the past.

Supporters and critics can agree that the nation is fortunate that its leader is a man prepared to cope with radically changed circumstances, a person of fixed principles but not one wedded to policies of the past.

In his first term, when many supposed that the clouded circumstances of his election would force Bush into a cautious, minimalist approach to governing, he boldly set out to recast many fundamental institutions and doctrines. At home, he engineered sweeping changes in the scale and distribution of taxes, redefined the relationship of the federal government to local schools and sponsored the largest expansion ever of Medicare. Policies for the environment, regulation of business, law enforcement and a dozen other fields were turned around.

Abroad, the changes were even more dramatic as Bush cast aside the doctrine of containment for one of pre-emptive action — applied unilaterally and controversially to Iraq. He encouraged an overhaul of the armed forces and he launched a style of diplomacy that rattled the teeth of many traditional allies.

Now, armed with a second and larger victory at the polls, his domestic agenda includes changing the Social Security system, reforming energy and immigration policies, reducing the number and scale of civil damage suits, simplifying the tax system and further changing public education.

Ambitious as this seems, the likelihood is that the world stage will demand more from Bush — and provide the sternest tests of his adaptability.

Iraq is a bleeding wound on his presidency, a war that growing majorities of Americans have joined the rest of the world in judging a mistake. The future of Iraq is less and less in America’s hands. Success in removing Saddam Hussein has been followed by failure to stabilize postwar conditions. The fate of that country will increasingly be settled by armed battles and political struggles among various factions in Iraq, who agree only on their desire to end the American occupation. As the president put it in an interview with The Washington Post last week, “Success in Iraq will depend upon the Iraqis defeating the enemy.”

A sketch of what else lies ahead for Bush can be found in “Mapping the Global Future,” a 120-page forecast of world affairs in the next 15 years, published last week by the National Intelligence Council, the CIA think tank.

“The international order,” it says, “is in the midst of profound change; at no time since the formation of the Western alliance system in 1949 have the shape and nature of international alignments been in such a state of flux as they have during the past decade. As a result, the world of 2020 will differ markedly from the world of 2004, and in the intervening years the United States will face major international challenges that differ significantly from those we face today. The very magnitude and speed of change resulting from a globalizing world — regardless of its precise character — will be a defining feature of the world out to 2020.”

One of the likely developments is the emergence of China, India and perhaps Indonesia as major economic and political powers, while Japan, Western Europe and Russia cope with the challenges of rapidly aging populations. The rise of Asian powers will likely be abetted by globalization — the rapid spread of technology — and pose a challenge to America’s economy.

The hopeful trend of democratization will likely confront opposition in ethnic and identity politics, especially the transnational force of Islamic extremism, and contribute to a “pervasive sense of insecurity.” Terrorism is likely to remain a threat, even if al-Qaida is demolished.

“The United States increasingly will have to battle world public opinion, which has dramatically shifted since the end of the Cold War,” the report says. At another point, it adds, “Growing numbers of people around the world, especially in the Middle East and the broader Muslim world, believe the U.S. is bent on regional domination — or direct political and economic domination of other states and their resources. In the future, growing distrust could prompt governments to take a more hostile approach … .”

Bush has his work cut out for him.

— David Broder is a columnist for Washington Post Writers Group.