Obama's gun control proposals have run into resistance in Congress, leaving their fate in doubt. Efforts by Senate Democrats to reach compromise with Republicans over expanding required federal background checks have yet to yield an agreement.
Majority leader Harry Reid brought gun control legislation to the Senate floor on Monday, though actual debate did not begin. He took the step after receiving a letter from 13 conservative Republican senators who said they would use delaying tactics to try to prevent lawmakers from even beginning debate on the legislation. Such a move takes 60 votes to overcome, a difficult hurdle in the 100-member chamber.
Further underscoring the tough road ahead for the Obama-backed legislation, a spokesman for Senate minority leader Mitch McConnell saidthat the Kentucky Republican would join the effort to block debate on the legislation if Reid tries to bring the measure to the floor.
There are 53 Senate Democrats and two independents who lean toward them, meaning Republican support ultimately will be needed to reach 60 votes to move ahead.
The conservative senators said the Democratic measure would violate the Second Amendment of the US Constitution which guarantees the right to bear arms, citing "history's lesson that government cannot be in all places at all times, and history's warning about the oppression of a government that tries."
"Shame on them," responded Reid. "The least Republicans owe the parents of those 20 little babies who were murdered at Sandy Hook is a thoughtful debate about whether stronger laws could have saved their little girls and boys."
On Monday, Obama returned to the state where a gunman killed 20 young children and six educators in Newtown last December in one of the worst school shootings ever in the US Connecticut state lawmakers last week passed one of the strictest gun control laws in the country.
Obama rode to the speech with Connecticut governor Dannel P Malloy, who signed his state's tougher gun control legislation into law Thursday with the Sandy Hook families standing behind him.
But legislation in Washington faces a tougher challenge, as the nation's memories of the shooting fade with time and the National Rifle Association, the influential gun rights lobbying group, wages a formidable campaign against Obama's proposals.
"The day Newtown happened was the toughest day of my presidency," Obama said in an emotional speech in Connecticut's capital Hartford, about 50 miles (80 kilometers) from Newtown. "But I've got to tell you, if we don't respond to this, that'll be a tough day for me too."
Some of the Sandy Hook families are making an attempt to push through the gun control legislation. Obama met with them privately before his speech at the University of Hartford Monday evening, then brought 12 family members back to Air Force One for the trip back to Washington. The relatives want to meet with senators who've yet to back the legislation to encourage their support in memory of their loved ones.
The White House lit up the steps of Air Force One with flood lights so photographers and television cameras could capture the image of Obama climbing the plane's steps with the families at dusk.
Nelba Marquez-Greene, whose 6-year-old daughter Ana was among the victims at Sandy Hook, held up a sign that said "Love Wins" as she walked toward the steps of Air Force One.
The families' lobbying trip was organized by Sandy Hook Promise, a nonprofit group started by community members in the wake of the shooting.
"Nothing's going to be more important in making sure that the Congress moves forward this week than hearing from them," Obama said in his speech. His eyes teared as he described Nicole Hockley, who lost her 6-year-old son, Dylan, saying how she asks him every night to come to her in her dreams so she can see him again.
"If there's even one thing we can do to prevent a father from having to bury his child, isn't that worth fighting for?" Obama asked.
Obama's speech was interrupted repeatedly by standing ovations from the packed gymnasium. At one point, the room erupted with chants of "We want a vote!" Audience members, many wearing green ribbons in support of the victims, stomped their feet and clapped their hands in unison with the chant.
Obama argued that lawmakers have an obligation to the children killed and other victims of gun violence to allow an up-or-down vote in the Senate that would only need 50 votes to pass.
"Some back in Washington are already floating the idea that they may use political stunts to prevent votes on any of these reforms," Obama said. "Think about that. 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. They're saying your opinion doesn't matter. And that's not right."
Obama said the vote shouldn't be about his legacy, but about the families in Newtown who haven't moved on to other matters.
"Newtown, we want you to know that we're here with you," Obama said. "We will not walk away from the promises we've made. We are as determined as ever to do what must be done. In fact, I'm here to ask you to help me show that we can get it done. We're not forgetting."
The proposal to expand background checks for gun buyers is considered to have the best chance of passage. Two influential senators, Democrat Joe Mancin and Republican Pat Toomey, are trying to work out an agreement that could expand background checks on firearms sales to include gun shows and online transactions.
Democrats were holding a lunchtime meeting Tuesday to assess whether the two senators had reached an acceptable compromise - or had a realistic chance of getting one.
An agreement between the two senators would boost efforts to expand background checks because it could attract bipartisan support. Abandoning those negotiations would put Democrats in a difficult position, making it hard for them to push a measure through the Senate and severely damaging Obama's gun control drive.
Federal background checks are currently required only for transactions handled by the roughly 55,000 federally licensed firearms dealers. Private sales such as gun show or online purchases are exempt. The system is designed to keep guns from criminals, people with serious mental problems, some drug abusers and others.
Gun control advocates consider expanded background checks to be the most effective step lawmakers could take to curb gun violence. The National Rifle Association and other critics say the checks are ignored by criminals, and they fear that expanding the system could be a step to the government maintaining files on gun owners.
With time running out on negotiations, the White House is making an all-out push this week. Vice president Joe Biden and attorney general Eric Holder planned to promote their plan at the White House on Tuesday with law enforcement officials. First lady Michelle Obama planned to wade into the debate Wednesday with a speech on youth violence in her hometown of Chicago.