The attacks were a one-two punch to an administration that has been relentlessly upbeat about its ability to tame the region.
Some conservative members of the Bush administration have argued that by establishing a friendly government in Iraq and taking a more aggressive stance on the Israeli-Palestinian conflict, the U. S. could solve a pair of problems that have bedeviled Bush's predecessors. Tuesday's events put both goals in jeopardy, at least for the moment.
Early in the day, on his way to the first golf outing of his August vacation, Bush had expressed optimism.
"A free Iraq will make the Middle East a more peaceful place, and a peaceful Middle East is important to the security of the United States," he said.
Less than two hours later, Bush was conferring heatedly with top aides about the Baghdad bombing. He went on the air shortly after noon, East Coast time, to denounce the bombers as "enemies of the civilized world."
In another two hours, the packed Jerusalem bus exploded.
Bush did not reappear for the rest of the day, and White House aides clung nervously to talking points and the president's earlier expressions of resolve.
"The attacks bring to light in a vivid way that terrorists are the enemies of the civilized world," White House Press Secretary Scott McClellan said gamely.
Administration officials said it was too early to determine the impact of the Jerusalem bombing on the Mideast peace plan known as the road map. Bush has taken the plan on as a personal cause and has a huge stake in its success.
National Security Council spokesman Sean McCormack insisted that the bombing should not be seen as the beginning of the end of the peace effort.
"Our commitment to help the parties reach the goals [of the road map] remains unchanged and unshaken," he said.
But former Middle East envoy Dennis B. Ross, who negotiated with the Israelis and the Palestinians during the Clinton administration, said the peace process could easily stall.
"Now everything is probably going to be frozen," he said, predicting that the Israelis will again insist, as they have for some time, that nothing can be accomplished until the Palestinian terrorist infrastructure is dismantled.
"My guess was the Israelis who were prepared to say, 'You don't have to arrest people' are now going to say, 'We must have a demonstration,' " Ross said.
As for the fate of the U.S. occupation and reconstruction of Iraq, Bush's televised remarks provided clues that the administration is beginning to fear that ordinary Iraqis are turning against the United States. Without their support, the U.S. intervention is likely to fail.
"Iraqi people face a challenge, and they face a choice," Bush said. "The terrorists want to return to the days of torture chambers and mass graves. The Iraqis who want peace and freedom must reject them and fight terror."
News of the Baghdad bombing arrived shortly after the president teed off at 7:30 a.m. By 8:15, the long lenses of TV cameras caught him talking into a cell phone, brow furrowed.
After conferring with a string of advisors, Bush cut short his round after the 11th hole and rushed back to his ranch. As he spoke before the television cameras, his face was tense as he argued that such attacks are a sign not of a failure of U.S. policy, but of its success.
"Every sign of progress in Iraq adds to the desperation of the terrorists and the remnants of Saddam's brutal regime," the president said. "Iraq is on an irreversible course toward self-government and peace."
Previous attacks in Baghdad did not appear to upset White House routine or White House confidence. When a car bomb killed at least 17 people at the Jordanian Embassy in Baghdad less than two weeks ago, Bush's public schedule did not change and the only public White House reaction was a brief statement from a junior spokeswoman.
But Tuesday's truck bombing in Baghdad clearly struck a nerve. And the Jerusalem bombing added to the concern, jeopardizing Bush's efforts to forge peace between Israel and the Palestinians.
In Washington, administration officials acknowledged they had many reasons to be gloomy.
For one thing, the Baghdad bombing was likely to dishearten Americans whose support is crucial for the reconstruction effort. Some experts have predicted that a large-scale attack might turn American public opinion against the intervention in Iraq.
"This is a terrible tragedy and it can't help but intimidate some people, even though our government's response will be to redouble our efforts," one State Department official said.
The bombing may also dishearten some of the countries that U.S. officials are trying strenuously to persuade to donate peacekeeping troops, an official said. The administration needs tens of thousands of additional troops so that war-weary U.S. units can return home.
At the Pentagon, officials worked late, fretting privately that new terrorist-style tactics against civilian targets would discourage help from both nongovernmental organizations and foreign troops.
"It is an attack on the international community," a senior defense official said, on condition of anonymity. "This is very clearly an attack to prevent a free and democratic Iraq."
Also a setback for the administration was the loss of U.N. mission chief Sergio Vieira de Mello, who had been highly effective in his post and, unlike some U.N. officials, had seen eye to eye with U.S. officials on many issues.
On a practical level, the bombing may increase the distance between Iraqis and those foreigners who are trying to rebuild the country by forcing the United Nations and nongovernmental groups to increase security. Until now, U.N. officials and others involved in the reconstruction had sought to distinguish themselves from U.S. military forces by interacting with Iraqis without bulletproof vests, weapons or armored vehicles.
There is some small room for optimism in both regions, some officials said.
The Jerusalem bombing could turn some Palestinians against militant groups like Islamic Jihad and Hamas -- both of which claimed responsibility for the attack -- making it easier for the Palestinian Authority to crack down on them.
Ross, the former Mideast envoy, said the best hope for progress would be the U.S. pushing each side to spell out specific actions it will take -- and pushing the Palestinian leadership to arrest members of Islamic Jihad and Hamas.
"I don't know how sustainable the process is going to be unless we see some action now," he said.
And in Iraq, the Baghdad bombing could wind up helping the administration if it makes U.N. members feel that they are united in the same cause with the Americans.
While many countries did not support the invasion of Iraq, none really wants to see the reconstruction effort fail.
"At the top level, this could draw leaders together. This could fortify the group. ... And it could turn out that for the bombers, attacking the U.N. was a really bad idea," one Pentagon official said.
But a senior State Department official acknowledged that the world's reaction can't be predicted until more facts are in. And in both conflicts, world reaction could cut either way.
If the outcome depends on Bush, his determination -- at least halfway through the double-whammy day -- appeared firm.
"By attempting to spread chaos and fear, terrorists are testing our will," Bush said in his televised address. "Across the world, they are finding that our will cannot be shaken. We will persevere through every hardship."
Reynolds reported from Crawford, Texas, and Richter from Washington. Times staff writers John Hendren and Sonni Efron in Washington contributed to this report.