"What choice do we have?" Mr Obama said at a vigil in the shattered Connecticut community. "Are we really prepared to say that we're powerless in the face of such carnage, that the politics are too hard? Are we prepared to say that such violence visited on our children year after year after year is somehow the price of our freedom?"
It was an unmistakable sign that he would at least attempt to take on the explosive issue of gun control. He made clear that the deaths compelled the United States to act, and that he was the leader of a nation that was failing to keep its children safe. He spoke of a broader effort, never outlining exactly what he would push for, but expressed outrage by yet another shooting rampage. "Surely we can do better than this," he said. "We have an obligation to try."
The massacre of 20 children and six adults at Sandy Hook Elementary on Friday elicited horror around the world, soul-searching in the United States, fresh political debate and questions about the incomprehensible - what drove the 20-year-old Adam Lanza to kill his mother and then unleash gunfire on children.
The grieving town was braced to bury the first two of the 20 small victims and debated when classes could resume - and where, given the carnage in the building and the children's associations with it. Education officials could not say whether the school would ever reopen. The district is considering eventually sending surviving pupils to a former school in a neighbouring town.
Mr Obama said: "Can we say that we're truly doing enough to give all the children of this country the chance they deserve to live out their lives in happiness and with purpose? I've been reflecting on this the last few days," the president said, sombre and steady in his voice. "And if we're honest with ourselves, the answer is no. We're not doing enough and we will have to change."
He promised to talk with law enforcement, mental health professionals, parents and educators on an effort to prevent mass shootings. The shootings have restarted a debate in Washington about what politicians can to do help - gun control or otherwise. Gun control advocates also say the latest shooting is a tipping point that could change the debate
The president first met privately with families of the victims and with the emergency personnel who responded to the shootings.
Police said Lanza was carrying enough ammunition to kill everyone in the school if given enough time. He shot himself in the head just as he heard police drawing near. The bullets were of the type designed to break up inside a victim's body and inflict the maximum amount of damage, tearing apart bone and tissue.
Lanza's mother was found dead in bed at home, shot four times in the head with a.22-calibre rifle. The killer then went to the school with guns he took from his mother and began blasting his way through the building.