Since his son died six weeks ago as collateral damage to a troubled young man’s wish for vengeance, Richard Martinez has been asked whom he holds responsible.

“I’m responsible,” the California lawyer answers, referring to most Americans’ failure to push harder to change gun laws after earlier mass shootings. “All those kids died and none of us did anything.”

Martinez is trying to make up for that now. On a six-month leave from his law firm, he’s traveling the nation to rally congressional support for tougher restrictions on gun sales, ownership and use.

Christopher Michaels-Martinez, 22, was one of six victims of Elliott Rodger’s May 23 shooting spree in Isla Vista, Calif., the location of the University of California at Santa Barbara. Rodger had vowed retribution because women didn’t find him attractive.

Chris, an only child, didn’t know the shooter, but he crossed paths with him at a deli. Chris died at the scene; Rodger later killed himself.

Chris had recently graduated as an English major from UC Santa Barbara and was heading to London in September for graduate studies.

Martinez’s grief and outrage were so raw in TV newscasts the day after the rampage that you wondered if he’d make it. “If I weren’t doing this, I don’t think I could survive,” he said last Tuesday in an interview at the Federal Building in Des Moines. “I have to do something to make my son’s death mean something.”

So he is traveling to Des Moines, Iowa, and Nashville, Tenn., Tallahassee, Fla., and Harrisburg, Pa., armed with postcards written by Americans pledging to only vote for candidates who support laws to reduce gun violence.

They’re “Gun Sense Voters,” a project of Everytown for Gun Safety. It launched the campaign after Martinez called on people to send politicians postcards saying “Not one more.” Nearly 2.5 million have been written by more than 625,000 people and are being hand-delivered to individual members of Congress and governors.

The group also aims to get a million voters to the polls on this issue.

Martinez hasn’t figured out exactly what the legislation should look like, but he says it must include background checks on all gun sales.

“There just hasn’t been a discussion in Congress about this,” he exclaimed. “After the massacre of all these little kids at Sandy Hook, those families supported legislation and it was defeated in the Senate by five votes. It didn’t even get to the House. I mean, 17 little kids died, the total body count was 27 and they didn’t do anything.”

He was “completely oblivious” to the issue, even after Sandy Hook. “It didn’t affect me. You don’t think it can happen to you. But 86 Americans are killed every day by guns in this country.”

Now Martinez has met relatives of 19 kids killed by guns from Aurora, Colo., to Tucson, Ariz. He told a congressman who called to offer sympathy, “I’m not interested in condolences. Do something.”

He met Peter Rodger, father of his son’s killer. Asked if he could forgive, Martinez said, “I can appreciate the difficulty a parent like Peter Rodger would face in dealing with a child who’s 22 years old and won’t do anything” — i.e., take medicine or get therapy for his mental health condition. “Also, I believe Peter Rodger is sincerely committed to making sure this doesn’t happen again. If he is genuinely committed, then that I can forgive.”

Chris’ mother, Karen Michaels, understands but finds it harder to forgive, Martinez said. She’s so devastated, she has trouble doing everyday things. Martinez, incidentally, is a defense attorney; Michaels is a prosecutor. She was 44 when Chris was born; he was 42. They are no longer a couple but remain close.

Outside the Federal Building, he introducing himself to protestors, some carrying pictures of loved ones lost to gun violence. They were with the Iowa chapter of Moms Demand Action for Gun Sense in America, part of the Everytown umbrella group, created in response to the Sandy Hook shootings.

Synice Miller held a picture of T.J. Gardner, her nephew who was killed in a drive-by shooting on the front porch of his Waterloo, Ia. home about a year ago. He was 24. “I wish they didn’t have guns,” she said. “I wish the war would stop. I wish people would stop killing and hurting one another. I just want peace.”

Martinez pulled a wagon holding postcards addressed to a U.S. senator and two congressmen from Iowa. All have resisted gun control legislation. All are Republicans, though Martinez insists this isn’t a partisan issue. He also knows it has many components, including untreated mental illness. But no other country has the gun violence we do, he said. “We’re Americans. I can’t accept that we can’t solve this problem.”

So a diverse group of survivors and new activists headed inside, through the metal detectors, to take their message to elected officials. They were led by a grieving father who says nothing else matters to him now, a father trying to make up for the time he lost not pushing for gun control, because he will never get back the time he lost with his child.

Rekha Basu is a columnist for the Des Moines Register.