Gabrielle Giffords tours European physics lab

Kelly also declined to comment on the Aurora, Colorado, movie massacre last Friday that killed 12 and wounded dozens of others. But soon after the killings he tweeted: "Gabby and I were horrified to hear of the tragedy in Colorado last night. Our thoughts and prayers are with the victims and their families."

Jared Loughner, a college dropout, was charged with first-degree murder in the attempted assassination of Giffords and other alleged crimes stemming from the shooting. He pleaded not guilty and was found mentally unfit to stand trial.

Democrat Ron Barber, Giffords' former aide who also was injured in the shooting that nearly took her life, won a June 12 special election to replace her in the U.S. House of Representatives, a victory she celebrated by hugging and kissing him on his forehead.