Speaking before families of the victims of the Sandy Hook massacre, President Obama made an impassioned and urgent plea for stricter gun laws, as he accused Republicans of threatening to use "political stunts" to block reforms.

"This is not about politics. This is about doing the right thing for all the families who are here that have been torn apart by gun violence," the president told a packed crowd at the University of Hartford, just 50 miles from the site of the December shooting in Newtown, Conn. "It's about them, and all the families going forward so we can prevent this from happening again. That's what it's about."

Obama's visit to Connecticut comes at the start of a critical week, as the Senate is expected to debate the president's gun control agenda. While there are signs of agreement to expand background checks, two major parts of the president's plan, a ban on assault-style weapons and high-capacity ammunition clips, seem unlikely to pass.

In a rousing, campaign-style speech the president warned lawmakers not to use political tactics to prevent the Senate from voting on gun reform measures, arguing that they have an obligation to the victims of gun violence.

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"If our democracy's working the way it's supposed to and 90 percent of the American people agree on something, in the wake of a tragedy, you'd think this would not be a heavy lift," Obama said of the broad support for background checks. "And yet some folks back in Washington are already floating the idea that they may use political stunts to prevent votes on any of these reforms."

Obama's warning comes as a group of 13 Republican lawmakers are threatening to block a vote on gun control legislation.

"They're saying they'll do everything they can to even prevent any votes on these provisions. They're saying your opinion doesn't matter and that's not right. That is not right," Obama said, as the crowd took to its feet, chanting "we want a vote!"

Nearly four months since the tragedy in Newtown, the president promised the parents of the slain children that "we will not walk away from the promises we've made."

"We want you to know that we're here with you," he said. "We are as determined as ever to do what must be done."

Before his remarks, the president met privately with several families of children who died in the Sandy Hook shooting. Many of those families then boarded Air Force One on their way to Washington to lobby Congress.

"If there's even one thing we can do to protect our kids, don't we have an obligation to try? If there's even one step we can take to keep somebody from murdering dozens of innocents in the span of minutes, shouldn't we be taking that step? If there's just one thing we can do to keep one father from having to bury his child, isn't that worth fighting for?" Obama said.