The memorial service, where the atmosphere was both mournful and convivial, was held to honor the 19 people shot last Saturday. Six, including a nine-year-old girl, a federal judge and a staffer for Giffords, were killed. Thirteen were wounded, including Giffords, who is still in the intensive care unit.
[TPM SLIDESHOW: Across the Nation, Vigils Held for Rep. Gabrielle Giffords]
Obama also addressed the waves of partisan that have been unleashed since the shooting, prompted in part by the Pima County sheriff, who blamed the political atmosphere for the violence.
And he called for civility.
"At a time when our discourse has become so sharply polarized -- at a time when we are far too eager to lay the blame for all that ails the world at the feet of those who think differently than we do -- it's important for us to pause for a moment and make sure that we're talking with each other in a way that heals, not in a way that wounds," he said.
"If, as has been discussed in recent days, their deaths help usher in more civility in our public discourse, let's remember that it is not because a simple lack of civility caused this tragedy -- it did not -- but rather because only a more civil and honest public discourse can help us face up to our challenges as a nation, in a way that would make them proud," he said. "It should be because we want to live up to the example of public servants like John Roll and Gabby Giffords, who knew first and foremost that we are all Americans, and that we can question each other's ideas without questioning each other's love of country, and that our task, working together, is to constantly widen the circle of our concern so that we bequeath the American dream to future generations."
(You can read his full prepared remarks here.)
Also speaking tonight were Homeland Security Secretary Janet Napolitano and Attorney General Eric Holder, who both read from the Bible, and Arizona Gov. Jan Brewer. The president of the University of Arizona, a student at the university and Daniel Hernandez, the Giffords intern who was the first to help her, spoke as well.
At the McKale Center before the service began, Obama met with the families of the victims of Saturday's shooting, as well as the first responders. They were issued special red VIP tickets by the university. He also went to the hospital, where he visited Giffords and her husband, Mark Kelly, as well as other injured victims and Giffords' staff and their families.
At the service, Obama told the crowd Giffords had opened her eyes for the first time just after he left.
The doctors who have been caring for Giffords attended the memorial service, and were greeted by a standing ovation when they entered the McKale Center.
The venue was filled to capacity with more than 14,000 people an hour before the service began, with overflow crowds of 10,000 filling the university's nearby stadium.