U.S. President Barack Obama speaks during a memorial service in Joplin, Missouri May 29, 2011. President Barack Obama visited Joplin on Sunday for a memorial for the victims and a first-hand look at the devastation from the tornado, rated an EF-5, or the strongest possible, and the deadliest single twister in the United States since 1947.

People attend a memorial service in Joplin, Missouri May 29, 2011. President Barack Obama visited Joplin on Sunday for a memorial for the victims and a first-hand look at the devastation from the tornado, rated an EF-5, or the strongest possible, and the deadliest single twister in the United States since 1947.

Residents of Joplin, Missouri, hold signs as U.S. President Barack Obama's motorcade passes during his visit in Joplin, Missouri, May 29, 2011. Obama travelled to Joplin, scene of last week's disaster, to inspect the tornado damage and participate in a memorial service.

Residents of Joplin, Missouri, hold flags as U.S. President Barack Obama's motorcade passes May 29, 2011. Obama travelled to Joplin, scene of last week's disaster, to inspect the tornado damage and participate in a memorial service.

Bibles are seen in boxes before a memorial service in Joplin, Missouri May 29, 2011 for victims of a tornado that struck a week ago. U.S. President Barack Obama promised victims of the deadliest U.S. tornado in 65 years that the federal government would help them rebuild, saying on Sunday it was a national tragedy.

People attend a memorial service in Joplin, Missouri May 29, 2011. President Barack Obama visited Joplin on Sunday for a memorial for the victims and a first-hand look at the devastation from the tornado, rated an EF-5, or the strongest possible, and the deadliest single twister in the United States since 1947.

U.S. President Barack Obama speaks to residents affected by tornado damage in Joplin