“Fight, fight, fight” were the first words by Gabrielle Giffords during a news conference on Wednesday from the same supermarket parking lot where a gunman opened fire on Jan. 8, 2011, wounding her and 12 others and taking six lives.

Ms. Giffords, a former congresswoman for Arizona, was embracing the role of constituent to her senators, Republicans John McCain and Jeff Flake, asking them to support legislation requiring background checks for every gun purchase.

“Be bold. Be courageous,” she urged them from behind a lectern. Onlookers cheered. Her husband, the former astronaut Mark E. Kelly, kept a supportive hand on her shoulder as she spoke. When she was done, he planted a kiss on her cheek.