From expansive executive privilege to hard-line tactics in the war on terrorism, Obama must decide what he'll undo and what he'll embrace.

The stakes couldn't be higher.

On one hand, civil libertarians and other critics of the Bush administration may feel betrayed if Obama doesn't move aggressively to reverse legal policies that they believe have violated the Constitution and international law.

On the other hand, Obama risks alienating some conservative Americans and some — but by no means all — military and intelligence officials if he seeks to hold officials accountable for those expansive policies.

These are some of the legal issues confronting him:

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• How does he close the Guantanamo Bay prison in Cuba? He's pledged to shutter it, but how quickly can he do so when it holds some detainees whom no administration would want to release?

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• Obama has declared coercive interrogation methods such as waterboarding unconstitutional and illegal, but will his Justice Department investigate or prosecute Bush administration officials who ordered or condoned such techniques?

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• Will the new administration press to learn the full extent of the Bush administration's electronic eavesdropping and data-mining activities, and will it curtail or halt some of them?

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• The Bush administration exerted tight control over the Justice Department by hiring more Republican-leaning political appointees and ousting those who were viewed as disloyal. Will Obama give the department more ideological independence?

Undoing some policies will take time.

With 316 conservative appointments to the federal courts over the last eight years, Obama could attempt to tilt the courts back to the center or even to the left with his nominees. He could alter the Supreme Court's bent by replacing two or three justices who'll probably retire soon.

Civil libertarians, who feel emboldened by a Democrat in the White House, tick off a long list of what they think Obama should do as soon as he takes office. Not only should Guantanamo be closed, they say, Obama should revoke the immunity for telecommunications companies that cooperated with secret eavesdropping, ban the use of secret prisons by the CIA and investigate and perhaps prosecute administration officials for authorizing controversial interrogation methods.

Anthony D. Romero, the executive director of the American Civil Liberties Union, which has led many of the challenges to the Bush administration's terrorism policies, said Obama could take action on most of these fronts "on day one" by issuing executive orders, such as closing Guantanamo.

"Unless he acts quickly, he runs the risk of showing the American people that their hope and optimism may have been misplaced, and reinforcing people's deep-seated cynicism that it's politics as usual in D.C.," he said.

Although Obama is likely to ban waterboarding and other aggressive techniques soon after taking office, prosecuting administration officials not only would be legally challenging because legislation has granted them immunity but also would be seen by Republicans as highly divisive.

Negotiating that minefield may be among the most difficult legal dilemmas Obama faces early in his administration because of pressure from the left and the right.

"There will be hell to pay if people are prosecuted," said Sanford Levinson, a University of Texas law professor. "But there'll be hell to pay if they just walk away scot-free."

He predicted that Obama might sidestep the controversy with the Bush administration's help. If President Bush issues pre-emptive pardons to prevent prosecutions, the Obama administration should form a bipartisan panel, similar to the Sept. 11 commission, to oversee an inquiry, he said. Once pardoned, officials implicated in the controversy would be required to discuss details of the policies because they'd be unable to assert their Fifth Amendment right to avoid self-incrimination.

The best person to lead such a commission? Levinson thinks it's John McCain, who condemned the interrogation techniques when he was running against Obama.

"There would be widespread support if the Obama administration did reach out to someone like McCain," Levinson said. "More people would regard it as not so much of a Democratic vendetta but as a necessary cleansing of an episode in recent American history that has had phenomenal costs to us around the world."

Democratic Sen. Dianne Feinstein of California, a senior member of the Senate Judiciary and Intelligence committees, predicted that Obama would move to close Guantanamo relatively quickly. She'll reintroduce legislation to do so early next year.

"The handwriting is on the wall," Feinstein said. "It's just a matter of time."

Although Guantanamo isn't expected to be as thorny as the issues of interrogation techniques, detention without charges and eavesdropping, it may take longer to close than Obama wants because of the question of what to do with high-value terrorists. The Obama administration could end up moving them to prisons scattered across the United States as it sorts out who should remain jailed and where others should be sent.

The Bush Justice Department chose to fight the court-ordered releases of many of the detainees, even those whom the military had cleared. Obama's attorney general is likely to soften that stance and begin releasing them with court oversight, or perhaps order new legal reviews of all detainees.

Three dozen district-court and 15 appellate court vacancies await. Appellate court decisions set precedents for multiple states. Whoever fills the vacant seat on the San Francisco-based 9th U.S. Circuit Court of Appeals, for instance, will shape the law covering nine Western states.

For this reason, appellate court vacancies can become battlegrounds. On the 4th Circuit Court of Appeals, which spans five states, including the Carolinas, a vacancy lingers after eight years.

Considerable speculation in the legal community has centered on potential female appointees to the Supreme Court, where Justice Ruth Bader Ginsburg is the only woman. One potential candidate is Judge Sonia Sotomayor, the first Hispanic woman to serve on the 2nd Circuit Court of Appeals. Another is Harvard Law School's Dean Elena Kagan, who like Obama was on the University of Chicago Law School faculty.

Noncourt appointments, too, can shape the law in important ways.

Whomever Obama appoints as attorney general and in other top positions in the Justice Department could move in new directions on hot-button issues such as gun control and immigration. And after pledging to tackle the financial crisis and concerns about global warming, Obama might dedicate more resources to prosecuting white-collar and environmental crimes.

Paul Charlton, one of the nine U.S. attorneys whom the Bush administration ousted, predicted that an Obama administration would take a different approach to the death penalty. Charlton clashed with Bush appointees who pushed prosecutors to seek the death penalty in a wide array of cases, including drug trafficking. "I expect there will be a more judicious use of the death penalty," he said.

However, Bush administration critics who hope an Obama White House will be the antidote to what they see as excessive executive power may be disappointed.

Gene Healy, a Cato Institute vice president and the author of the book "The Cult of the Presidency: America's Dangerous Devotion to Executive Power," said expanding presidential power was a bipartisan reflex.

"People tend to think more positively about having robust executive authority when they're the ones who are actually wielding the authority," he said.

Obama, however, is unlikely to be aggressive as Bush. "He'll probably seek congressional approval, and that may be more effective at growing executive power than the unilateral, go-it-alone approach," Healy said.