Even as he comforts a shaken country, aides say, Bush is determined not to let the national tragedy of the space shuttle Columbia imprison him or his agenda.
Then he turned to the Sept. 11, 2001, terrorist attacks, conjuring memories of that catastrophe, which is more directly related to Bush's top priorities than is Saturday's space shuttle disaster.
"The kind of men who would seize planes filled with innocent people and crash them into buildings," Bush said, "would not hesitate to use biological or chemical or nuclear weapons. They wouldn't hesitate at all."
Any president must perform a careful balancing act when confronted by a national calamity - soothing the collective pain but also seeming strong, clear of vision and able to concentrate on the nation's pressing problems.
Especially for Bush, the space shuttle accident came at a time already freighted with significance, as he faces two huge challenges - the possibility of war against Iraq and a stubbornly sluggish economy - that could define him as a leader and the ultimate success of his presidency.
Secretary of State Colin L. Powell, as scheduled, will travel to the United Nations tomorrow to present what administration officials say is intelligence that Iraq possesses weapons of mass destruction and that Hussein has links to terrorists.
The Columbia disaster also came two days before Bush was to issue his new federal budget plan, a document that he sent to Congress yesterday and that largely enumerates his priorities as president.
One senior White House official called it Bush's "responsibility to the country" to ensure that, as he guides the nation through a period of mourning, he does not become distracted from issues that he has described to Americans as vitally important.
"When you are the president of the United States, you always face a number of challenges - some of which you choose, and some of which you accept," the official said.
Asked why Bush, 48 hours after the space shuttle broke apart, decided to hold an unrelated event in Maryland, the official said: "Life continues on."
The president tried to signal yesterday that he could simultaneously manage a crisis and press on with his agenda.
But the president neither canceled nor delayed his trip to Bethesda, which was intended to highlight a program in his new budget plan called "Project BioShield."
The initiative, projected to cost $6 billion over 10 years, would speed up research into new vaccines to guard against biological or chemical attacks.
It would also authorize the administration to research and swiftly distribute vaccines for diseases such as smallpox, anthrax and botulinum toxin, without congressional approval.
"We already have the knowledge and ability to manufacture some of the vaccines and drugs we need, yet we have had little reason to do so up until now, because the natural occurrence of these diseases in our country is so rare," the president said.
"But the world changed on Sept. 11, 2001. And we've got to respond to that change."
Only in the first moments of his 15-minute speech did Bush address the space shuttle. He said America was "reminded again of the sacrifices made in the name of scientific discovery."
In a speech of more than 2,000 words, the president dedicated 126 to the space shuttle tragedy.
To be sure, Bush has hardly completed his role as comforter in chief.
He will speak in Houston today at a memorial service for the seven lost astronauts, eerily recalling memories of President Ronald Reagan's role in the same city at a similar event in 1986, honoring the seven crew members who perished on the space shuttle Challenger.
In a memorably stirring eulogy, Reagan vowed to continue sending shuttles into space.
"Every family member I talked to asked specifically that we continue the program - that that is what their departed loved one would want, above all else," Reagan said then.
"We will not disappoint them."