WASHINGTON - Barely 100 days in office, President Barack Obama is facing his first domestic emergency with the outbreak of swine flu and is seeing yet again how fresh challenges can erupt from the unlikeliest of places.

In the space of a month, he has had to deal with a North Korean missile launch and a hostage drama involving Somali pirates half a world away.

And now, from Mexico, comes a new flu that has killed up to 149 people south of the U.S. border but has not had the same deadly force in the United States, sickening at least 65.

If there is any clear tendency he has demonstrated in his response to all of these challenges, it is that he has responded to all of them with an abundance of caution.

He denounced the missile launch as provocative but made no sudden moves. The Somali pirate crisis played out over four days before U.S. snipers killed three pirates and freed the hostage American freighter captain.

In the case of this swine flu, Obama has walked a fine line, appearing concerned but trying not to generate panic among Americans already on edge from the weak U.S. economy.

This is obviously a cause for concern and requires a heightened state of alert. But it is not a cause for alarm, Obama said on Monday.

He has dispatched key officials to offer reassuring words to anxious Americans, including White House homeland security adviser John Brennan, the secretary of the Homeland Security Department, Janet Napolitano, and Richard Besser, acting director of the Centers for Disease Control.

Napolitano said the number of confirmed swine flu cases is likely to rise in the next few days, but that we are confident in the efforts underway across the federal government and across state and local governments to keep Americans safe and healthy.

White House Chief of Staff Rahm Emanuel, in a CNBC interview on Tuesday, was careful to point out to his interviewer that the government's approach to dealing with swine flu should not be considered a crisis response.

THE UNEXPECTED

That's a fair question, but I think this is very sensitive at this moment. I think you have a public health concern. That's first and foremost, he said.

Challenges come in fast and furiously at the White House, unexpectedly from any and all directions, and a president's response can define his time in office.

Nobody is suggesting at this time that the swine flu outbreak presents as serious a problem as, say, the Katrina hurricane in 2005. Time will tell.

Emanuel did say he had read John M. Barry's book, The Great Influenza, about the 1918 flu outbreak that began auspiciously in the spring, went underground, then erupted with full force in the fall.

What happens next is chiefly up to the virus, Barry wrote in The New York Times on Tuesday. But it is up to us to create a vaccine as quickly as possible.

Ken Wainstein, who was homeland security director for President George W. Bush and now at the law firm O'Melveny & Myers, said the swine flu outbreak was an example of how White House officials have to deal with unanticipated challenges while coping with other issues.

In this case, much of the groundwork for preparing for a potential pandemic has been in place for several years because of previous concerns about the issue.

It really is something that demands a strong interagency response, a high level of coordination, Wainstein said.

Norman Ornstein, a political expert at the American Enterprise Institute, said the unexpected event is an inherent feature of the White House.

You're almost always going to basically deal with the possibility that there will be some other crisis that emerges just as you're juggling other balls. Obama seems ready to do that compared to other presidents, Ornstein said.

But it would help, he added, if Obama had more members of his relevant team in place, since some key players are not yet in place at the Department of Health and Human Services.

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