The U.S. invasion of Iraq began on March 20, 2003. As American troops raced toward the Iraqi capital of Baghdad, special correspondent Mike Cerre was embedded with the 2nd Battalion, 5th Marines known as FOX 2/5. He takes a look at what the war and invasion meant for those U.S. troops and what they have been battling since. It's the start of a NewsHour series looking at the war, 20 years later.