While most political scientists subscribe to the rally-round-the-flag idea, some wonder if it will be quite so straightforward this time, as Bush confronts Kerry -- a war hero and senator with a lengthy foreign policy resume -- and potential negative momentum on Iraq.
"Because Iraq has now been identified as a problem spot, Bush is less likely to gain sympathy or the benefit of the doubt should things go horribly wrong," says Greenberg, who generally backs the rally-round-the-flag scenario. "With 9/11, nobody saw it coming."
Morris P. Fiorina, a political science professor at Stanford University and senior fellow at the Hoover Institution in Palo Alto, Calif., thinks that rather than boosting Bush's public esteem, another major terrorist attack on a U.S. target "could be the kiss of death" for the president.
"I don't think there would be any automatic rally-around-the-flag effect in the event of another domestic terror attack" or an attack on a U.S. target overseas, says Fiorina, who has written about the impact of electoral forces. "The Democrats could say the administration wasted billions of dollars and hundreds of American lives in Iraq while Osama bin Laden ran loose."
An attack on a non-U.S. target, such as a foreign ally, could be a different story, Fiorina believes: "You revive the real danger [of terrorism in voters' minds] without suffering the cost ourselves."
However, Polsby and others say Americans likely would rally around Bush after another terror attack.
Dennis W. Johnson, associate dean at the graduate school of political management at George Washington University in Washington, D.C., and a former Democratic political consultant, believes Bush would surge initially after a terror attack, but could face a backlash within weeks or months, depending upon the circumstances.
"If it's perceived that this is something that we should figure out, or it seems our homeland security people should have figured out, then of course it goes against the president," Johnson says.
As with terrorism, Fiorina believes the less Iraq is in the news, the better things will be for Bush.
"I think there are worse and better scenarios, but there is little that gives you any positive" politically for Bush, Fiorina says.
Johnson says Iraq could play strongly for Bush if weapons of mass destruction finally are found -- or more modestly if there is a peaceful handover to Iraqi authorities.
Chaos in Iraq, or a major battlefield tragedy with large loss of American life, could do serious damage, he says.
"If it turns to chaos, you're going to start asking yourself, 'Well, why were we there in the first place?' " Johnson says. "If you see that in June -- the handing over from [America's civil administrator] Paul Bremer to the provisional council or whatever -- and you see the next month the entire country is aflame … that's not how you want to exit."
Johnson believes Bush could face even more political risk if U.S. forces get caught in a severe flare-up between North and South Korea.
People might think, "Here he is playing the cowboy as diplomat, he's talking tough, and look what has happened," Johnson says.
While experts disagree on who ultimately gains politically in the event of a terror attack or foreign crisis, they agree Bush gets a big boost if America or its allies catch the master terrorist himself -- Osama bin Laden. But again, timing might be key.