WASHINGTON (AP) – In a whirlwind week of change, President Barack Obama jettisoned Bush administration policy on greenhouse gases, shone an unforgiving light on its support for torture as an interrogation tactic and eased its restrictions on Cuba.

But there are limits, even to this new president’s power, and a campaign pledge to seek a ban on assault weapons is an early casualty as a result.

And while the promise of change was arguably Obama’s single most powerful asset in last year’s campaign, the week demonstrated anew how carefully he calibrates its impact.

“We have been through a dark and painful chapter in our history,” the president said in a statement that accompanied the release of once-secret memos outlining torture techniques the Bush administration allowed.

“But at a time of great challenges and disturbing disunity, nothing will be gained by spending our time and energy laying blame for the past.”

That was designed as a reassurance to the CIA employees who carried out waterboarding, which simulates drowning, and the other harsh interrogation techniques that former President George W. Bush once sanctioned and that Obama has now banned – much as his decision to leave combat troops in Iraq a few months longer than he once promised was a bow to the Pentagon.

“I will always do whatever is necessary to protect the national security of the United States,” he said in a statement on the torture memos that could easily have been written about the troop withdrawal.

Attorney General Eric Holder added one more assurance, announcing the administration would pay legal expenses for anyone in the intelligence agency who needs a lawyer as a result of carrying out interrogations covered by the memos.

Holder also formally revoked every legal opinion or memo issued during Bush’s presidency that justified interrogation programs, a largely symbolic step since Obama had already said his administration would not rely on them.

The release of the documents had been the subject of a long, fierce debate, with a deadline looming as the result of a lawsuit brought by the American Civil Liberties Union.

No lawsuit drove the timing of the new Cuba policy, which was released in the run-up to Obama’s first presidential trip to Central America. And here again, Obama went further than some wanted and not as far as others had hoped.

Under the new policy, the administration lifted restrictions on Cuban-Americans who want to travel and send money to their island homeland and freed U.S. telecommunications companies to seek business there.

Some of the changes specifically undid what Bush had imposed: tightened travel restrictions on Americans wishing to visit relatives in Cuba; limiting payments to immediate family; and bans on seeds, clothing, personal hygiene items, veterinary medicines and – later – cell phones from humanitarian parcels.

But the broader embargo remains in place as it has since the Kennedy administration, its existence meant now as then to prod the Cuban government into democratic reforms.

In response to the announcement, Cuban President Raul Castro said he is ready to put “everything” on the table in talks with Americans, including questions of human rights and political prisoners. If so, that would mark a change from decades of Cuban insistence that those issues were not subject for discussion.

Secretary of State Hillary Rodham Clinton pronounced Castro’s comments an overture, and said, “We are taking a very serious look at how we intend to respond.”

Still, despite sentiment within the 15-member Caribbean Community to lift the U.S. embargo, Jamaica’s prime minister, Bruce Golding, said the organization had agreed not to push Obama too hard on the issue.

By contrast, there was little that was nuanced about the Environmental Protection Agency’s announcement Friday that carbon dioxide and five other greenhouse gases emitted by cars and many industrial plants “endanger public health and welfare.”

It was prompted by a Supreme Court ruling two years ago that said greenhouse gases are pollutants under the Clean Air Act and must be regulated if found to be a danger to human health or public welfare.

Confronted with the high court’s decision, the Bush administration stalled, leaving for Obama an issue he was only too happy to seize. EPA Administrator Lisa Jackson said while the agency is prepared to move forward with regulations under the Clean Air Act, the administration would rather defer to Congress.

“The (EPA) decision is a game changer,” said Rep. Ed Markey, D-Mass., who is involved in drafting legislation to limit greenhouse emissions.

For all the changes Obama has piled up since taking office 87 days ago, his retreat on assault weapons is hardly unique. He has already yielded on other relatively minor issues, giving in to veterans groups during the budget debate, for example.

Pressed by Mexican President Felipe Calderon to help stem the flow of military-style assault weapons from the United States, Obama said he still believed that the ban made sense. And yet, he added: “None of us are under any illusion that reinstating that ban would be easy.” He said he would focus instead on using existing laws to stop the flow of weapons prized by elements of the Mexican drug trade.

If anything, Obama’s closest allies in Congress are probably relieved.

Speaker Nancy Pelosi of California signaled as much several weeks ago after Holder said the administration wanted to renew a ban that lapsed and that the powerful National Rifle Association opposes strenuously.

“One good place to start would be to enforce the laws that are on the books right now,” she said on Feb. 26. “And I think the evidence points this out, that the Bush administration was not enforcing law.”

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EDITOR’S NOTE – David Espo has covered politics and government for The Associated Press for more than 25 years.

AP-ES-04-18-09 1215EDT