Mark Barden, whose son Daniel was among those killed in the Newtown massacre, has said families of the victims are heartbroken at the Senate's blocking of gun ownership legislation but will continue to campaign for stronger weapon controls.
He issued an emotional plea at the White House after a plan aimed at expanding background checks for gun buyers failed to receive enough support in a vote.
With President Obama looking on, Mr Barden said: "We always knew this would be a long road. We don't have the luxury of turning back."
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Theresa May has launched her bid to become the next leader of the Conservative Party.
The government is set to announce that David Cameron's successor will make the decision on whether to expand Heathrow or Gatwick.
Michael Gove is to stand for the Conservative Party leadership, saying he does not believe Boris Johnson can "provide the leadership".