Washington - In his first week as commander in chief, President Barack Obama tried to send the nation and world two messages about American security:

One, that he will do things very differently than George W. Bush did.

Two, that he can keep America safe and strong while doing so.

In a flurry of executive orders and public statements, Obama made the case last week that America can roll back hard-line Bush policies without sacrificing its security.

Not only that, he suggested that an America that gets along better with the world and doesn't overreach in the war on terrorism is a stronger, not a weaker nation.

Whether Obama can deliver on that argument will go a long way toward determining the success of his presidency. For while the economy dominated the Obama transition, he and his advisers know that they will be judged as much if not more on their ability to prevent another attack on U.S. soil and manage threats and crises abroad.

"Earlier generations faced down fascism and communism not just with missiles and tanks, but with sturdy alliances and enduring convictions," Obama said Tuesday in his inaugural address. "They understood that our power alone cannot protect us, nor does it entitle us to do as we please. Instead they knew that our power grows through its prudent use; our security emanates from the justness of our cause, the force of our example, the tempering qualities of humility and restraint."

Safety and ideals

Two days after that speech, the new president visited the State Department to signal his commitment to diplomacy and issued executive orders reversing a bundle of Bush security policies. The orders closed CIA detention facilities, directed the closing of the Guantanamo prison within a year, halted military commission trials at Guantanamo and required that the interrogation of detainees follow the Army Field Manual, which doesn't allow for some of the harsh methods that have been used by the CIA in recent years. The order did not end the practice known as "rendition," sending some suspects to other countries, but Obama officials said there would be no renditions to countries that use torture.

Obama said he wanted to restore "the standards of due process and core constitutional values that make this country great even in the midst of war," echoing his inaugural address, when he declared that "we reject as false the choice between our safety and our ideals."

In other words, Obama argued that in repudiating controversial Bush security policies, he wasn't reducing U.S. defenses, but making "our security stronger," as White House press secretary Robert Gibbs contended. And that a more humble and restrained America would be no less single-minded and relentless about defeating its enemies.

Prudence and power

"For those who seek to advance their aims by inducing terror and slaughtering innocents, we say to you now that our spirit is stronger and cannot be broken - you cannot outlast us, and we will defeat you," Obama said in his inaugural address.

The central thrust of these arguments - that in some cases tougher is weaker, prudence is power, nicer is stronger - will now be tested not in the give-and-take of the campaign but in real-world outcomes on Obama's watch.

Republicans have made it clear they will measure Obama by his ability to keep the nation attack-free, as Bush did in the time since Sept. 11, 2001.

Bush "was right to strengthen the military and intelligence and to create new tools to monitor the communications of terrorists, freeze their assets, foil their plots, and kill and capture their operators," former Bush strategist Karl Rove wrote in the Wall Street Journal last week in a closing defense of the Bush presidency. "These tough decisions - which became unpopular in certain quarters only when memories of 9/11 began to fade - kept America safe for seven years and made it possible for Mr. Obama to tell the terrorists on Tuesday, 'We will defeat you.' "

The Obama view, in a few cases even shared by his GOP opponent John McCain, was that some hard-line Bush policies undermined U.S. security by alienating others around the world and damaging America's standing. McCain also joined Obama during the campaign in arguing for more effective use of diplomacy and alliances.

Guantanamo dilemma

Obama's new policies face important questions. In the case of Guantanamo, the new president is moving deliberately and has deferred any decision on what to do with the most difficult class of detainees at the camp: those who pose clear dangers but can't be tried in U.S. courts because of inadmissible evidence or other issues. He has tasked a high-level panel to make recommendations on that question.

"It's one thing to say you're going to close (Guantanamo), quite another to say what you're going to do with them," Senate Minority Leader Mitch McConnell (R-Ky.) said at a National Press Club event Friday.

In the case of the executive orders, Obama was acting quickly to make good on campaign promises and to signal a sharp change in direction after Bush.

But the campaign promise that undoubtedly will be most scrutinized in its execution will be the one to pull out combat forces from Iraq within 16 months.

The day after his inauguration, Obama met with the U.S. commander and ambassador in Iraq to discuss plans for "a responsible military drawdown."

In this case, Obama's challenge will be to fulfill his campaign pledge without a relapse in Iraq toward the levels of civil warfare that preceded the U.S. troop surge launched by Bush in early 2007.

At a conference Friday in Washington, D.C., military expert Stephen Biddle of the Council on Foreign Relations described Iraq as being in the "early stages of the negotiated end to a pretty intense civil war," a process he said was historically "highly volatile and very unstable."

"The central mission of the U.S. presence in Iraq today is to serve as classical peacekeepers," said Biddle, who said both Obama's timeline for withdrawal and the timeline in the recent status of forces agreement between the U.S. and Iraq would create challenges when it comes to preventing a reversion to earlier levels of violence.