He arrived at the police station here early, as usual. Two officers were standing in the locker room admiring a new .45-caliber semiautomatic pistol. Thinking the chamber was empty, one of them pulled the trigger. A bullet ricocheted off a locker and went right through the boy’s neck, severing his spinal cord.

At 16, he would never walk again and never fulfill his dream of becoming a police officer.

Now, three decades later and seven terms into his career as one of Rhode Island’s two members of the House of Representatives, Mr. Langevin, 48, is the only quadriplegic ever to serve in Congress. And his story, unknown to many of those who work with him every day in the Capitol, has thrust him into the raging national debate over gun control.

For the past month, he has been on a quiet campaign to persuade his colleagues to give up their guest passes to next Tuesday’s State of the Union address by President Obama so that victims of gun violence can attend.