WASHINGTON – Emboldened by a sweeping election victory, President Bush heads into his second term with an ambitious agenda to change America and the world.

Four years after he came to office in a disputed election, Bush on Wednesday finally claimed the mandate that eluded him the first time. He’s the first president to win a popular-vote majority since 1988 and he rolled up more votes than any president in history, even though his margin over John Kerry was well short of a landslide.

White House officials interpreted his 51 percent majority, and Republican gains in the House of Representatives and Senate, as a call to action and an affirmation of the president’s far-reaching goals.

After just two hours sleep in the pre-dawn hours Wednesday, Bush began the day by reaching out to newly elected Republican senators for their help with his second-term plans.

“Now is the time to get it done,” Bush told Sen.-elect Jim DeMint of South Carolina in one of a series of Wednesday morning phone calls.

Over the next four years, Bush intends to set Iraq on the road to democracy, defeat global terrorism and send a wave of freedom across the Middle East. At home, he plans to extend his tax cuts to future generations, revamp the nation’s legal system, bring free-market capitalism to Social Security, enact a producer-friendly energy policy and overhaul the federal tax system.

If he succeeds, he’ll leave office in January 2009 with a legacy that would rank him among America’s most effective presidents. If he fails, he could be remembered as a flawed leader whose ambitions exceeded his abilities and plunged America into lasting turmoil and debt. Often, “second terms are a stumbling ground,” said historian Robert Dallek on Wednesday, as the second terms of Richard Nixon, Ronald Reagan and Bill Clinton make clear.

Bush has made it clear, publicly and privately, that he has no intention of going out with a quiet, steady-as-she-goes second term. By his calculations, he has two years to push his ambitious domestic agenda through Congress before his power wanes and attention shifts to the next presidential election.

Some potential trouble spots are obvious. North Korea and Iran seem intent on pushing ahead with nuclear programs despite international pressure. Tensions between China and Taiwan are increasing. In Russia, President Vladimir Putin is turning away from democratic reforms and consolidating power in a worrisome way.

The possible deaths of ailing Palestinian leader Yasser Arafat and an increasingly frail Fidel Castro in Cuba could cause more problems – or offer new opportunities.

Personnel issues at home also will push their way onto the presidential agenda. Supreme Court Chief Justice William Rehnquist, who has thyroid cancer, is a likely candidate for retirement during Bush’s second term, and several other aging justices may follow suit. Any appointment that would tip the court’s ideological balance would almost certainly trigger a bitter confirmation fight in the Senate.

White House counsel Alberto Gonzalez, who came to Washington with Bush from Texas, remains a top a contender for a Supreme Court slot.

Some top Cabinet officials will view Bush’s re-election as a signal that it’s time to move on to more lucrative, less demanding jobs in the private sector. Attorney General John Ashcroft, Homeland Security Secretary Tom Ridge, Transportation Secretary Norm Mineta and Health and Human Services Secretary Tommy Thompson head the list of officials who are expected to lead the second-term exodus.

“We can expect about half of the Cabinet and sub-Cabinet will be gone by June,” said Paul Light, a professor of public service at New York University and a leading expert on White House personnel issues.

Any second-term shakeup in Bush’s national security team – Defense Secretary Donald Rumsfeld, Secretary of State Colin Powell and national security adviser Condoleezza Rice – would spark an intense power struggle over the direction of U.S. foreign policy.

Vice President Dick Cheney and Rumsfeld have been the leaders of the neo-conservative faction that pushed hard for war with Iraq; Powell is the chief in-house spokesman for the so-called realists, who favor a more-nuanced approach to foreign policy and greater emphasis on diplomacy.

Powell seems the most likely to leave, although some speculate that he may hang on to avoid ceding the field to Rumsfeld. Rice, one of Bush’s most trusted advisers, could conceivably replace either of them if she doesn’t return to academia.

But with Cheney remaining, U.S. policy in a second term seems likely either to continue on its present course or become more aggressive and less conciliatory – especially if Powell departs.

Bush’s economic team, led by Treasury Secretary John Snow and budget director Joshua Bolten, is expected to remain largely intact after the 2002 shakeup that started with the ouster of former Treasury Secretary Paul O’Neill. However, a sweeping attempt to change the tax code is possible.

Bush intends to meet with his Cabinet on Thursday before spending a quiet weekend at Camp David, the presidential retreat in Maryland.

Of all the unknowns facing Bush in a second term, Iraq looms as the most worrisome. The next big test will come about the time Bush takes the oath of office for a second time on Jan. 20. His promise to hold national elections in Iraq in late January will likely be tested by terrorist attacks, spreading chaos and power struggles among Iraq’s various ethnic and religious groups.

A successful election would help put Iraq on the path to stability, but a disputed outcome could embolden insurgents and terrorists and further divide the country. Continuing problems and a rising American death toll could make Iraq Bush’s Vietnam in a second term, draining his political clout and casting a pall over his presidency.

Even if things go well overseas, budget realities at home will complicate Bush’s efforts to push his agenda through Congress. Budget projections show massive federal deficits for the foreseeable future, raising the bar for almost any proposal that costs money. Nevertheless, a push to extend or expand Bush’s tax cuts is almost certain.