US Independence Day

President Barack Obama welcomes military families to an Independence Day celebration on the South Lawn of the White House in Washington, Monday, July 4, 2011. (AP Photo/Charles Dharapak)

President Barack Obama and first lady Michelle Obama walk down the South Portico staircase to welcome military families to an Independence Day celebration on the South Lawn of the White House in Washington, Monday, July 4, 2011. (AP Photo/Charles Dharapak)

President Barack Obama and first lady Michelle Obama welcome military families to an Independence Day celebration on the South Lawn of the White House in Washington, Monday, July 4, 2011. (AP Photo/Charles Dharapak)

President Barack Obama and first lady Michelle Obama welcome military families to an Independence Day celebration on the South Lawn of the White House in Washington, Monday, July 4, 2011. (AP Photo/Charles Dharapak)

President Barack Obama picks up a child as he greets military families at an Independence Day celebration on the South Lawn of the White House in Washington, Monday, July 4, 2011. (AP Photo/Charles Dharapak)

Fireworks light up the night sky behind the Gateway Arch and the Old Courthouse Monday, July 4, 2011, in St. Louis. (AP Photo/Jeff Roberson)

People play in the Swann Memorial Fountain, at Logan Square, in view of City Hall, right, after an Independence Day celebration Monday, July 4, 2011, in Philadelphia. The U.S. celebrated the 235th anniversary of the signing of the Declaration of Independence. (AP Photo/Matt Rourke)

Michael McDonald performs with The Roots during an Independence Day celebration Monday, July 4, 2011, in Philadelphia. (AP Photo/Matt Rourke)

Spectators watch the fireworks display over the Hudson River, Monday, July 4, 2011, in New York. A portion Manhattan's west side is closed to vehicular traffic, allowing pedestrians to camp out and wait for the 40,000 shells launched after dusk from a barge on the river. (AP Photo/John Minchillo)

Spectators watch the annual Independence Day fireworks over the Hudson River, Monday, July 4, 2011, in New York. A portion Manhattan's west side is closed to vehicular traffic, allowing pedestrians to camp out and wait for the 40,000 shells launched after dusk from a barge on the river. (AP Photo/John Minchillo)

Spectators watch fireworks explode over the Hudson River from 42nd street during Macy's annual 4th of July fireworks show on Monday, July 4, 2011 in New York. (AP Photo/Bill Kostroun)

Leslie Phillips, center, of Dalton, Ga., relaxes near American flags she placed in the sand on Monday, July 4, 2011, in Perdido Key, Fla. (AP Photo/Mark Humphrey)

Julia Jones, 5, spins a glow stick during a fireworks display in Alachua, Fla., on Monday, July 4, 2011. (AP Photo/The Gainesville Sun, Matt Stamey)

Light from Independence Day weekend fireworks is reflected in the water in front of the Bellagio Hotel as they explode over Caesar's Palace on The Strip, Sunday, July 3, 2011, in Las Vegas. (AP Photo/Julie Jacobson)

Tourists watch Independence Day weekend fireworks explode over Caesar's Palace as the Bellagio fountain show plays simultaneously, Sunday, July 3, 2011, in Las Vegas. (AP Photo/Julie Jacobson)

Spectators wave flags as the USS Constitution fires its cannons off Castle Island in Boston on its annual 4th of July turn around in Boston Harbor, Monday, July 4, 2011. (AP Photo/Michael Dwyer)