(USA TODAY) -- With several GOP lawmakers threatening to block a vote on Democratic-backed gun-control legislation, President Obama used a speech in Connecticut on Monday to charge that his opponents are threatening to use "political stunts" to prevent an overhaul of gun laws.
Obama's stinging rebuke came as 13 GOP lawmakers sent a letter to Senate Majority Leader Harry Reid on Monday, indicating they would block legislation "that would infringe on the American people's constitutional right to bear arms, or on their ability to exercise this right without being subjected to government surveillance."
Late Monday, a spokesman for Senate Minority Leader Mitch McConnell said the Kentucky Republican would join the filibuster if Reid moves forward with the gun bill.
"They're not just saying they'll vote 'no' on ideas that almost all Americans support," Obama said in a speech at the University of Hartford, just 50 miles from the site of the December mass shooting at Sandy Hook Elementary School that reignited the debate over the nation's gun laws. "They're saying your opinion doesn't matter. And that's not right."
With the Senate set to begin debate on new gun measures as soon as this week, it remains uncertain how much of Obama's broad gun-control agenda - laid out less than a month after the tragedy in Newtown, Conn. - will be enacted.
The current version of the Senate gun bill would strengthen current laws on gun trafficking and straw purchasers, increase grants for improvements in school safety and expand background checks to nearly every gun purchase.
Sens. Chuck Schumer, D-.N.Y., Joe Manchin, D-W.Va., and Mark Kirk, R-Ill., have been working for months to put together support for compromise background check legislation that would allow unchecked purchases for certain private gun transfers. Sen. Patrick Toomey, R-Pa., is the latest Republican to consider signing onto the legislation and continues to negotiate with Manchin on the details of the bill. But no deal has yet been reached
Measures to bar high-capacity magazines and military-style assault weapons - crucial parts of Obama's original package - have been left out of the main bill and are expected to be voted on as amendments.
Still, the gun bill is facing increasing opposition from the GOP.
"Senators have an obligation both to uphold the Constitution and to promote solutions that effectively address national problems," said Sen. Mike Lee, R-Utah, one of the 14 who have threatened a filibuster. "The current gun-control proposals fail both tests."
Reid also expressed frustration on Monday with the Republican senators and called on them to rescind their threat to block votes.
"I'm deeply troubled that a number of my Republican colleagues went so far as to send me a letter saying we will agree to nothing, there will be no debate, there will be nothing, we want you to do zero on anything dealing with stricter gun measures," Reid said. "There is simply no reason for this blatant obstruction except for the fear of considering anti-violence proposals in full view."
The White House said Obama traveled back to Connecticut on Monday - he hadn't been in the state since a vigil held days after the tragedy for the 20 young children and six educators who died in the Sandy Hook Elementary School tragedy - to call on Americans to put pressure on Congress to act.
After his speech, Obama returned to Washington on Monday night with 11 family members of Sandy Hook victims who planned to lobby lawmakers on Capitol Hill to take up the president's gun agenda. The White House extended the invitation to the Sandy Hook families so they could attend Obama's speech and still get to Washington in time to meet lawmakers, according to White House press secretary Jay Carney.
In recent weeks, Obama's traveled to Denver, Chicago and Minneapolis to amplify to try to win public support for his gun-control agenda. But Obama has left much of the heavy lifting of pushing his legislation to Vice President Biden, and senior aides.
On Monday, Obama chafed against the suggestion that failure to pass significant parts of his gun legislation would amount to a political failure for him.
"This isn't about me," Obama said. "And it shouldn't be about politics. This is about doing the right thing for families like yours that have been torn apart by gun violence, and families going forward."