President Barack Obama has accused Republicans of stooping to political stunts to block gun reform, in a fervent appeal delivered close to the site of the Newtown school massacre.
At a critical moment for hopes for sweeping action to stem gun violence, Obama travelled on Monday to Hartford, Connecticut, not far from Sandy Hook Elementary School where 20 children and six adults were gunned down in December.
In sharp, impassioned remarks, he contrasted the courage of parents whose children were killed by a deranged gunman with US lawmakers he said feared the wrath of the powerful American gun lobby.
"Some folks in Washington are already floating the idea that they may use political stunts to prevent votes on any of these reforms," Obama told a raucous crowd during his second gun control rally in a week.
"They're not just saying they'll vote no on ideas that almost all Americans support. They're saying they'll do everything they can to even prevent any votes on these provisions.
"What's more important to you: our children or an A-grade from the gun lobby?"
As Congress returns from a recess, some Republicans have pledged to use Senate filibuster tactics to prevent a gun reform bill likely to be placed before lawmakers in the next few weeks from coming to a final vote.
They have said that a package prepared by Democratic Senate Majority leader Harry Reid would infringe the constitutional right to bear arms.
Obama has been delivered increasingly emotive calls for action - surrounded by gun violence victims and police officers to build pressure on Republicans to relent.
The president contrasted the bravery of Nicole Hockley, mother of 6-year-old Dylan who was killed at Sandy Hook, who has become a vocal campaigner for gun control with the behaviour of his political foes in Washington.
"If Nicole can summon the courage to do that - how can the rest of us do any less?" Obama asked the 3,100 strong crowd.
Obama, noting that victims' families refer to the December 14 killings as "12-14" in the same way those bereaved on September 11, 2001 refer to "9-11," said the day of the Sandy Hook massacre was the worst of his presidency.
"I got to tell you, if we don't respond to this, that'll be a tough day for me too, because we've got to expect more from ourselves and we've got to expect more from Congress.
Joining Obama on Air Force One later to head back to Washington to begin an intense lobbying effort were 12 family members of victims of the Newtown shootings.
The president pledged to use all the power of his office to enact measures to stem violence after December's killings, but as their memory has faded, the tricky politics of Washington has chipped away at his reform package.
His calls for a revived ban on assault weapons and limits on high capacity magazines appear unlikely to pass Congress, and doubt clouds the prospects of another plan - for expanded background checks for gun owners.
Republican Senator Mike Lee said Monday that 13 senators have now signed a letter objecting to Reid's legislation and threatening to filibuster it.
"The proposals serve primarily to limit the rights of law-abiding citizens, while doing little, if anything, to reduce violent crimes," Lee said.
Obama also has problems from some Democratic senators hailing from conservative or rural states - who have testing re-election races in 2014 and are wary of more gun control.
The president is now concentrating on background checks that would bar felons or the mentally ill from owning weapons, as intense negotiations take place on Capitol Hill.
In one bipartisan effort, Democratic pro-gun Senator Joe Manchin and Republican Pat Toomey are reported to be working on a measure that would require background checks for all gun purchases.
The plan would however exempt sales between close family members and some hunters in an attempt to undercut some Republican opposition.