US President Barack Obama's sweeping gun-control package faces an uncertain future in Congress, where majority Republicans in the House of Representatives are rejecting his proposals while the president's allies in the Democratic-controlled Senate are stopping well short of pledging immediate action.
Obama's $500 million plan marks the most comprehensive effort to tighten gun laws in nearly two decades as he tries to build on the high emotions over last month's school shooting in Connecticut, where a gunman with a legally purchased high-powered rifle left 20 young children and six adults dead. Obama has called that day the worst of his presidency.
The president's announcement on Wednesday appealed to both common sense and conscience, but frustrated observers of Congress say the growing partisan divide there is little swayed by either.
"To make a real and lasting difference, Congress must act," Obama said. "And Congress must act soon."
Obama must try to push through an assault weapons ban and other sensitive measures through a Congress that is already busy preparing for fights over three looming fiscal deadlines and a debate over comprehensive immigration reform.
The country's most powerful pro-gun lobby, the National Rifle Association, is already rejecting many of Obama's proposals as it insists on an absolute reading of the Constitution's Second Amendment-guaranteed right to possess and bear firearms.
The group, which also represents a gun industry that since the Civil War has promoted a national gun culture, has long warned gun owners that Obama wants to take their guns away.
Critics counter that the country's founding fathers never could have foreseen assault weapons more than two centuries ago, when guns were intended for the common, not individual, defense, guns were often stored in community areas and rifles fired one shot at a time.
The issue went overseas Thursday when Defense Secretary Leon Panetta spoke to U.S. troops in Europe.
"Who the hell needs armor-piercing bullets except you guys in battle?" Panetta told soldiers in Italy. "For the life of me, I don't know why the hell people have to have assault weapons."
Panetta, who said he believes in the Second Amendment and has been a longtime hunter, was asked about the issue by a soldier who wanted to know what steps the Obama administration was going to take that "don't have to do with tearing apart our Second Amendment."
The head of the National Rifle Association on Thursday morning said the organization has no problem with tighter background checks of gun purchasers, another key Obama proposal.
But David Keene told CBS that too much emphasis has been placed on banning certain firearms and said officials should focus instead on the "devastatingly broken mental health system in this country."
Earlier this week, the NRA posted an online video that called Obama an "elitist hypocrite" for allowing his daughters to be protected by armed Secret Service agents while not embracing armed guards for schools. A White House spokesman called the video "repugnant" and "cowardly."
The fate of Obama's gun plan could ultimately hinge on a handful of moderate Democratic senators. Although they are unlikely to endorse the president's call for banning assault weapons, they might go along with other proposals, such as requiring universal background checks on gun purchases and limiting ammunition magazines to 10 rounds or less.
Several of these senators responded warily after Obama unveiled his proposals.
"I will look closely at all proposals on the table, but we must use common sense and respect our Constitution," said Sen. Jon Tester. The Democrat told the Missoulian newspaper in his home state recently that he supports background checks but doesn't think an assault weapons ban would have stopped the Connecticut shootings.
Seeking to circumvent at least some opposition in Congress, Obama signed 23 executive actions Wednesday that don't require lawmakers' approval, including orders to make more federal data available for background checks and end a freeze on government research on gun violence.
But he acknowledged that the steps he took on his own would have less impact than the broad measures requiring approval from Congress.
"I will put everything I've got into this, and so will Joe," the president said, referring to his vice president. "But I tell you, the only way we can change is if the American people demand it."
Republican leaders in the House of Representatives have made clear they'll wait for the Senate to act first, since they see no need to move on the contentious topic if it doesn't.
"House committees of jurisdiction will review these recommendations. And if the Senate passes a bill, we will also take a look at that," said Michael Steel, spokesman for House Speaker John Boehner.
Senate majority leader Harry Reid, a Democrat and gun-rights backer who's been supported by the NRA in the past, responded cautiously, saying he was committed to ensuring the Senate considers legislation on gun violence early this year. He didn't endorse any of Obama's proposals.
Many rank-and-file Republicans criticized Obama's proposal. "The right to bear arms is a right, despite President Obama's disdain for the Second Amendment," said Rep. Tim Huelskamp.
Senators are expected to begin discussions on how to proceed when they return to Washington next week from a congressional recess, according to a Democratic leadership aide who requested anonymity to discuss internal deliberations.
They could end up breaking the president's proposals into individual pieces, with votes possibly starting next month.
While the assault weapons ban is seen as having little if any chance of passage, support may coalesce behind requiring universal background checks, which is a top priority for advocacy groups that see it as the most important step to curbing gun crimes.
The Brady Campaign to Prevent Gun Violence says 40 percent of gun sales are conducted with no criminal background checks, such as in some instances at gun shows or by private sellers over the Internet. Obama would seek to require checks for all sales.
Sen. Chuck Schumer, a Democrat, already has sponsored a bill to require universal background checks that the Senate could take up, while Sen. Frank Lautenberg, another Democrat, has legislation banning ammunition magazines with more than 10 rounds.
Despite the uncertainty in Congress and opposition from the powerful NRA, outside groups are encouraged by polling showing public support for change.
A lopsided 84 percent of Americans back broader background checks, according to a new Associated Press-GfK poll. Nearly 6 in 10 Americans want stricter gun laws, the same poll showed, with majorities favoring a nationwide ban on military-style weapons.
"Now it's up to us," said Dan Gross, president of the Brady Campaign. He said his group would be working "to bring that voice to bear in this process, because without that, it's not going to happen."