For hours, Gabrielle Giffords had been working the halls of Congress, walking with difficulty or being pushed in her wheelchair. She and her husband, Mark Kelly, zigzagged through the marble corridors the day after the president’s State of the Union speech, visiting top lawmakers to try to sway them in the nation’s raging debate over gun violence.

Leaving the office of Senate Majority Leader Harry M. Reid (D-Nev.), Kelly pivoted his wife toward two doors that opened to the Senate floor. They wanted to go inside for a few minutes to peek at the action.

“This is only for members of Congress,” said a Senate guard, blocking the way. Kelly started to explain, but the guard cut him off. “Only members of Congress allowed.” Kelly turned his wife’s wheelchair toward another hallway.

It was a curt symbol of what Giffords has lost in the two years since a gunman shot her in the head as she was meeting with constituents outside a Tucson supermarket on a bright Saturday morning. Days into her third term as a moderate Democratic congresswoman, her life as a politician was ended. Yet, almost as suddenly, the same kind of random and horrible violence has propelled her into a whole new world.

Since the school massacre in Newtown, Conn., Giffords has emerged as the country’s most famous victim advocate, the face of a renewed effort across the country to legislate gun control. It is impossible to be near Giffords and not be reminded of her injuries.

Former congresswoman Gabrielle Giffords (D-Ariz.) urged Congress to act on gun violence during a Senate hearing on Jan. 30. Giffords was shot and injured two years ago while meeting with constituents in Tucson, Ariz. (JulieAnn McKellogg/The Washington Post)

But she has lost neither her sharp political instinct nor her determination to deliver her message. When asked during her visit to Capitol Hill if she might be more powerful in her new role, her answer was swift and firm.

“Yes,” she said. “Impact.”

Yet the question is whether the former congresswoman can change the seemingly in­trac­table opposition on Capitol Hill to new restrictions on assault weapons, high-capacity magazines and loopholes in background checks. The sides in the debate have long been chosen, and few members of Congress will cross the powerful gun lobby to support the kinds of changes that Giffords advocates.

In short, in her new role, will Gabby Giffords have an impact?

If not, it won’t be for lack of trying. She and Kelly have embarked on a full-scale campaign to try to reduce gun violence. They have created an advocacy group, Americans for Responsible Solutions, raised a considerable chunk of money and brought their message to Washington, where Giffords was once regarded as a rising political star.

Their partnership works like this: Kelly does most of the talking. Giffords sits or stands beside him, animated and smiling, offering a word here and there. It is not what Giffords says in her new role as much as what she cannot say. Her message is mostly silent, a reminder that no one, even a member of Congress, is immune from the random violence that can transform — or end — a life.

“Gabby has particular insight into the issue, being a former member of Congress, a victim of gun violence, a gun owner and a strong supporter of the Second Amendment,” Kelly, a former astronaut and space shuttle commander, said. “I think folks want to hear what she has to say about this.”

A reporter shadowing Giffords and Kelly last week saw the extent of Giffords’s injuries from the Jan. 8, 2011, shooting in Tucson — and her commitment to overcome them.

Last Tuesday, the couple awoke at 5 a.m. in Tucson and flew seven hours across the country to attend President Obama’s State of the Union address. They were both invited to sit in the House gallery as guests of Arizona lawmakers.

But before the address, they held a fundraiser for their gun-control group, which they say represents a more moderate voice in the gun debate.

Inside a packed, trendy Capitol Hill restaurant, Kelly told more than 150 donors about how he woke up with jet lag in the middle of the night during a trip to China last December and looked at his BlackBerry.

“It didn’t take me long to realize that 20 kids had been murdered,” Kelly said. “I got on the phone with Gabby. Gabby said we have to stop talking and do something.”

The crowd broke out in applause. The crush of people moved in closer to meet Giffords, dressed in a taupe jacket and black pants. Kelly stood close at her side.

Everyone wanted to shake her hand, hug her, tell their story or praise her courage. Giffords, 42, who always loved this aspect of politicking and was engaged in exactly such give-and-take when she was shot, was in her element.

“Thank you very much,” Giffords said to each donor. When she spotted someone she knew, she squealed in delight and said their name.

“Whoa, CJ!” she said, hugging a former aide.

“Ron!” she called out to Rep. Ron Barber, her former Tucson office director who was also shot and was elected to her seat in Congress last November.

Giffords continues to undergo speech and physical therapy. Close friends and colleagues believe that her personality and comprehension are intact. But the aphasia that she suffers as a result of her brain injury sometimes prevents her from speaking in full sentences, and the right word often proves elusive. When she appeared before a Senate hearing late last month, she delivered a powerful and emotional statement. One good friend described her as a “caged bird.”

For a long time after her injury, Giffords spoke one word, sometimes the wrong one. Then, two words. Now, sometimes three or four words spill out at a time.

Rep. Debbie Wasserman Schultz (D-Fla.), a close friend, emerged to hug Giffords, who touched Schultz’s blond curls, which had recently been trimmed.

“Short hair,” she said.

Wasserman Schultz introduced a teenager named Megan Hobson. She was caught in a gang-related crossfire in Miami and spent three weeks in a coma.

Giffords had been smiling for an hour. Her face suddenly fell. Looking down at Megan, she took her hand in hers.

“You’re very strong,” Giffords told her.

After a couple of hours, Kelly extracted his wife from the crowd. “She enjoyed that beforehand and she still does,” he said.

Kelly led Giffords to a black Suburban. She struggles to walk. She is partially blind and her right leg and arm are mostly paralyzed. She held Kelly’s hand, swinging her right leg to the side to move forward slowly. She wore a leg brace and black tennis shoes.

Inside were three aides and her service dog, Nelson. The dog, half Lab and half golden retriever, has been her constant companion for four months.

Kelly and Giffords hadn’t had a chance to eat at the fundraiser, so a restaurant employee handed them a big paper bag full of pizza, shrimp and crab cakes on the way out.

“Want another piece of pizza?” Kelly asked his wife.

“One more piece,” she answered immediately.

The Suburban passed the Longworth House Office Building, where she had her office. Giffords looked wistfully into the darkness. Five heavily armed police officers waited at the entrance to the Capitol, its dome gleaming behind them.

“Gabrielle Giffords is inside,” said Pia Carusone, the executive director of Giffords’s new group. An officer looked inside.

“Hello!” Giffords said, shrugging her shoulders playfully and smiling at him. He waved and motioned the Suburban on.

At the door, another police officer waited. He had been on the patrol sent to guard Giffords in Texas, where she initially recovered after she was shot.

Her face lit up when she saw him and she called out his name.

“Gabby, do you want the wheelchair?” Kelly asked her.

“No,” she said. “I’ll walk.

Giffords and Kelly were whisked into a back elevator and up to the office of House Minority Leader Nancy Pelosi (D-Calif.). While they waited for the State of the Union to start, a parade of lawmakers, celebrities and visitors came by to see Giffords. Eventually Giffords and Kelly joined a reception that Pelosi was hosting.

“Hello,” said a man who approached Giffords with his wife. “Good to see you again.”

Giffords and Kelly smiled but did not appear to recognize the couple.

“We met you in Newtown,” the man said. “Our daughter was Grace.”

Grace McDonnell was one of the children killed inside Sandy Hook Elementary School. Kelly and Giffords had traveled to Newtown after the shooting to meet with the parents of victims.

Giffords’s smile disappeared, and she reached out to the woman, Lynn McDonnell. Kelly responded: “You gave us Grace’s picture. We keep it next to our microwave and look at her every day.”

Two hours later, Giffords and Kelly stood in the House gallery as Obama, nearing the end of his speech, spoke of gun violence and called out her name. Kelly’s teenage daughters, Claudia and Claire, were at their side, wearing green Newtown ribbons.

“These proposals deserve a vote,” Obama said. “Gabby Giffords deserves a vote.”

Giffords cannot clap anymore. She held her mostly paralyzed right hand with her left hand and shook them up and down.

They got back to Pelosi’s office at 10:40 p.m. Giffords’s aides were busy at a table tweeting the night’s news under a hashtag they created on the spot: StandwithGabby.

“Are you tired, Gabby?” Kelly asked her.

“Yes, I’m tired,” she replied.

“I know you’re worn out,” he said, hugging her.

On Wednesday morning, Giffords rode the Capitol elevator up to meet with House Majority Leader Eric Cantor (R-Va.). She joined the legions of lobbyists and advocates who come to press their desires.

Cantor emerged from his office to greet her.

“Oh, hello, hello, hello,” she said.

Giffords moved forward with Kelly and two aides, her right arm in a sling, walking slowly, swinging her motionless leg forward over the oriental rugs, past the chandeliers and into Cantor’s ornate inner office. She sat down. Kelly did most of the talking.

When it was clear that she could not serve again in Congress and Giffords stepped down a year ago, she walked to the House rostrum and handed her letter of resignation to Speaker John A. Boehner (R-Ohio). He brushed away tears as he kissed her goodbye.

But the speaker, like other Republican leaders in Congress, will be an extremely hard sell on any kind of gun control. His long-standing support of gun rights has earned Boehner an “A+” rating from the National Rifle Association. Recognizing his importance, Giffords had saved the visit until the end of her day.

“You can see from the reaction of the full House and Senate last night that people are thinking about this issue,” Kelly said outside the speaker’s office. “And I believe most members, probably all of them, agree we have to do something. But, this is a process. What did you use to say about the legislative process, Gabby? It’s like making something, remember?”

“Sausage,” Giffords said as her aides laughed.

“Yes, you don’t want to see the inner workings,” Kelly said.

“Meeting with the speaker of the House and the Senate majority leader is a big deal,” Kelly said.

“Yes, big deal,” Giffords repeated.

“We’re a team,” Kelly said.

“We’re a team,” Giffords said. “Both of us.”

In the last few minutes before going into Boehner’s cavernous office, Giffords stood off to the side with an aide, practicing a few words. Ever the politician, she understood better than anyone the value of talking points, of a simple message distilled to its essence.

“Support more background checks!” she said softly and insistently. “Support more background checks.”

At 3:30 sharp, the House speaker emerged from his office.

Giffords looked up at him.

“Boehner!” she said excitedly.

“Come in,” said Boehner.

He reached out to shake Giffords’s one good hand.