A year ago, as they took office, Donald Rumsfeld and George W. Bush came to a kind of understanding. America, the two men agreed, was seen around the world as "gun-shy" and averse to taking risks. This perceived vulnerability in the nation's posture, they believed, was weakening the effectiveness of US military deterrents.
It had to change, they decided. "He and I concluded that whenever it occurred down the road that the United States was under some sort of a threat or attack, that the United States would be leaning forward, not back," Defense Secretary Rumsfeld recalled recently.
Then came Sept. 11. Taking the offensive, the Bush administration decided, publicly at least, to keep all options for military action on the table, Rumsfeld says. In essence, demonstrating US military willpower emerged as a key, underlying imperative of the war on terror. US casualties, Rumsfeld stressed, would not weaken American resolve.
Washington's more aggressive posture - combined with widespread public support for military action following the biggest terrorist attack on American soil, - appears to be eroding the decades-old "Vietnam syndrome," experts say.
Americans overwhelmingly - 92 percent - endorse military force in the war on terror, according to a Pew Research Center survey released Tuesday. Strong US majorities now also back the use of military force to combat the terrorist threat beyond Afghanistan - including in Iraq (73 percent), Sudan (73 percent), and Somalia (65 percent) - even, in the case of Iraq, if it means America could sustain thousands of casualties, the poll shows.
Still, this increased willingness by the public to put US troops in harm's way is not unconditional - nor is it necessarily permanent, experts say.
Today, Americans back the war on terror because it is seen as more vital to US security than other military actions in the post-cold-war era, experts say. As the antiterror campaign continues in pursuit of shadowy enemies in remote, lawless regions of the world, it could become more complicated to link it clearly to US interests.
"Terrorists breed in areas where the state is very weak," potentially drawing US forces into civil wars or nation-building roles more peripheral to the hunt for terrorists, says Gordon Adams, director of security policy studies at George Washington University here. "Do they play a direct combat role if there is internal civil strife? This question will be posed repeatedly in Somalia, or Sudan, or Indonesia, or other places where there is a gray area between state power and terrorists."
Meanwhile, American tolerance for troop casualties remains largely untested. In recent years, the growing capability of the US military to conduct precision air wars and take other actions that sharply limit its losses creates an expectation that American combat deaths will remain minimal.
"It's still a very mixed message," says William Quandt, a Middle East expert at the University of Virginia and a former National Security Council official. "We fought the Afghan campaign just as we did in the Gulf [War in 1991], which was to minimize casualties to a remarkable degree."
"We still don't know what would happen if we got into another Vietnam-like situation - a large-scale, bogged-down conflict where we aren't sure of our interests," he says. "Iraq is one of those cases where this could be tested. Iraq will be a big challenge."
Nevertheless, from the first days of the conflict in Afghanistan, the Pentagon has cautioned US citizens - and the world - to expect more than isolated airstrikes and "cruise-missile diplomacy," experts say.
"The cruise missiles and bombers are not going to solve this problem. We know that," Rumsfeld said on Oct. 8, the day after the strikes began.
Bristling at any suggestion of an "antiseptic" war, administration officials warned Americans that US casualties were inevitable - a recognition, analysts say, that it was wiser publicly to overplay the risk than to underplay it.
To America's adversaries, Rumsfeld vowed that even major US casualties would not "frighten the United States off their track" - thus addressing terrorists' musings about earlier incidents, such as the 1983 truck bombing in Lebanon that killed 241 marines and sailors and hastened a US withdrawal.
Moreover, the Pentagon repeatedly refused to rule out any US military option - including ground troops.
Rumsfeld indicated, without making a direct comparison, that he wanted to avoid what he saw as President Clinton's mistake in rejecting from the start the use of US ground troops in the 1999 Kosovo conflict.
Indeed, Rumsfeld pushed to position teams of several dozen US Special Operations Forces with Afghan opposition fighters, voicing impatience when bad weather delayed the plans. Later, he approved the landing of hundreds of US marines to set up a base in southern Afghanistan.
By exposing Americans to direct ground combat in Afghanistan, Washington showed that it was "leaning forward" - but only to a degree, some critics say.
Within the White House and military establishment, there remains "an enormous concern about the public perception of casualties, at home and abroad," demonstrated in the failure to use more ground troops, more aggressively, says Dan Goure, a senior fellow at the Lexington Institute, a nonpartisan defense think tank here.
"It was a big mistake, because they have to get [Osama] bin Laden and the Al Qaeda leadership," agrees Ivan Eland, a director of defense studies at the CATO Institute here.
Other defense experts, however, argue that the military has used the right balance of US troops and Afghan forces. "Getting the Taliban or Osama bin Laden is a surgical operation that relies on intelligence," says Mr. Adams of George Washington University. "A massive ground force would have been much too clumsy."