President Barack Obama is calling on Americans to raise their voices against the gun violence that has rattled the nation several times during his time in office, saying it "falls upon us to make it different."

President Barack Obama (3rd L) and first lady Michelle Obama (R) attend a memorial service for victims of the Washington Navy Yard shooting at the Marine Barracks (Alex Wong/Getty Images)

Obama spoke at a memorial service Sunday for the 12 men and women killed in the Washington Navy Yard last week. The president and first lady Michelle Obama also visited with the victims' families.

Obama says it has become clear that change will not come from politicians in Washington, who have been unable or unwilling to change the nation's gun laws even when tragedy strikes the capital city. Instead, Obama says, change will have to come the only way it ever has — from people demanding action.

Reprising his role of the nation's consoler in chief after yet another mass shooting, Obama issued a call to action on gun control measures that failed to pass earlier this year and show no new momentum in the wake of last week's rampage at a military installation just blocks from the Capitol.

"Our tears are not enough," Obama told thousands gathered to mourn at the Marine Barracks. "Our words and our prayers are not enough. If we really want to honor these 12 men and women, if we really want to be a country where we can go to work and go to school and walk our streets free from senseless violence without so many lives being stolen by a bullet from a gun, then we're going to have to change."

Obama said when such senseless deaths strike in America, "it ought to be a shock to all of us, it ought to obsess us. It ought to lead to some sort of transformation."

NRA: Get 'homicidal maniacs' off streets

WASHINGTON (AP) — Gun rights supporters are calling for greater efforts to identify and lock up mentally ill people who are dangerous. That's in response to the recent Washington Navy Yard shootings.

National Rifle Association official Wayne LaPierre told NBC's "Meet the Press" Sunday not enough of the mentally ill are being committed to psychiatric hospitals.

He said "homicidal maniacs" left on the street are "going to kill."

Aaron Alexis, the IT contractor who killed 12 people inside a Navy Yard building last week, had a history of violent outbursts and was being treated for serious mental problems. He was able to exploit weaknesses in federal laws aimed at keeping guns out of the hands of the mentally ill.

Legislation to expand background checks on gun purchasers is stalled in the Senate.

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