Campaign manager Jim Messina sent an email to Obama supporters Thursday urging them to sign a petition backing the president's proposals and promising "more soon" from the organization.
Obama, seeking to sidestep some congressional opposition, also signed 23 executive actions Wednesday, 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 Capitol Hill. He is also calling for limiting ammunition magazines to 10 rounds or less.
"To make a real and lasting difference, Congress, too, must act," Obama said.
The question now is how and whether that happens.
House GOP leaders 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 to House Speaker John Boehner.
Many rank-and-file Republicans scorched Obama's proposal. "The right to bear arms is a right, despite President Obama's disdain for the Second Amendment," said Rep. Tim Huelskamp, R-Kan.
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.
The argument went trans-Atlantic Thursday when Defense Secretary Leon Panetta, who is leaving the administration, talked to U.S. troops in Europe.
"Who the hell needs armor-piercing bullets except you guys in battle?" Panetta told the soldiers at the U.S. Army Garrison Vicenza in northern 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 duck hunter, was asked about the issue by a soldier who wanted to know what steps the Obama administration was going to take to deal with attacks in schools that "don't have to do with tearing apart our Second Amendment."
Known for his often blunt and colorful language, Panetta added that things can be done to protect children "so that the nuts that are out there won't use these kinds of weapons to wipe them out."
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, D-N.Y., already has sponsored a bill to require universal background checks that the Senate could take up, while Sen. Frank Lautenberg, D-N.J., has legislation banning ammunition magazines with more than 10 rounds.
Senate Majority Leader Harry Reid, D-Nev., a gun-rights backer who's been supported by the National Rifle Association 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.
Despite the uncertainty on Capitol Hill and opposition from the powerful NRA, outside groups are encouraged by polling showing public support for changes to the law. They intend to try to harness that sentiment to pressure lawmakers.
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."
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AP White House Correspondent Julie Pace contributed to this report.