At the same time, gun control groups were staging a "Day to Demand Action" with more than 100 rallies and other events planned from Connecticut to California. This was on top of a $12 million TV ad campaign financed by New York City Mayor Michael Bloomberg that has been pressuring senators in 13 states to tighten background-check rules.
But if political momentum was building after the nightmarish December shootings, it has flagged as the Senate prepares to debate gun restrictions next month. Thanks to widespread Republican resistance and a wariness by moderate Democrats from Southern and Western states including six who are facing re-election next year a proposed assault weapons ban seems doomed and efforts to broaden background checks and bar high-capacity ammunition magazines are in question.
In one statement that typifies moderate Democrats' caution, spokesman Kevin Hall said Virginia Sen. Mark Warner is "still holding conversations with Virginia stakeholders and sorting through issues on background checks" and proposals on assault weapons and magazines.
In stronger language this week, Democratic Sen. Heidi Heitkamp of North Dakota said, "I do not need someone from New York City to tell me how to handle crime in our state. I know that we can go after and prosecute criminals without the need to infringe upon the Second Amendment rights of law-abiding North Dakotans."
Expanding federal background checks to private sales at gun shows and online is the gun-control effort's centerpiece and was the focus of Obama's remarks. The system, designed to block criminals and the mentally disturbed from getting firearms, currently applies only to transactions by licensed gun dealers.
The National Rifle Association opposes the expansion, citing a threat that it could bring federal registries of gun owners, which would be illegal. The NRA says what is needed is better enforcement of the existing system, which it says criminals too easily circumvent.
Democratic sponsors are sure to need 60 votes to prevail a daunting hurdle since the party has just 53 of the Senate's 100 seats, plus two Democratic-leaning independents. In a sign of potential trouble ahead, six Democrats backed a failed GOP proposal last week that would have required 60 votes for all future bills restricting guns.
"The week after Newtown, we thought it would be a tough road to 60 votes but we'd get there," said Mark Glaze, director of Mayors Against Illegal Guns, a group that Bloomberg helps lead. "Three months after Newtown, it looks like a tough slog but we'll get there."
Exactly how they can achieve that has yet to be demonstrated, with Obama's turn Thursday as arm-twister-in-chief underscoring the political pressure that proponents feel is needed 104 days after the Newtown killings.
"Now's the time to turn that heartbreak into something real," said Obama. While not naming the NRA, he chided opponents for trying to "make all our progress collapse under the weight of fear and frustration, or their assumption is that people will just forget about it."
NRA officials are unyielding in their opposition, with spokesman Andrew Arulanandam saying, "We have a politically savvy and a loyal voting bloc, and the politicians know that."
Obama and his backers find themselves in an unusual position struggling to line up votes for a proposal that polls show the public overwhelmingly supports.
An Associated Press-GfK poll in January found 84 percent support for expanding background checks to include gun show sales. Near-universal checks have received similar or stronger support in other national surveys.
Polls in some Southern states have been comparable. March surveys by the Quinnipiac University Polling Institute found more than 9 in 10 people in Florida and Virginia backing expanded background checks, the same margin found in February by an Elon University Poll in North Carolina.
Analysts say politicians are loath to alienate the people who oppose broader background checks and other gun restrictions because they tend to be dedicated, single-issue voters.
The polling also points to a broader context that politicians are watching: The same Quinnipiac polls that show one-sided support for gun restrictions show people closely divided over whether Obama or the NRA better represents their views on guns.
"They can be for a specific kind of gun control, but they may be suspicious of efforts of other kinds that they think might come down the pike," said Peter Brown, the Quinnipiac poll's assistant director.
Sens. Chuck Schumer, D-N.Y., Joe Manchin, D-W.Va., and Mark Kirk, R-Ill., have spent weeks negotiating with GOP senators, hoping to find a formula that could win the needed bipartisan support.
"I'll wait and see the outcome of that," Sen. Mark Begich, D-Alaska, said of those talks, adding that the message his constituents give him is, "Don't take away our rights, our individual rights, our guns."
Other moderate Democratic senators who could be tough for supporters of broader background checks to persuade include Heitkamp of North Dakota, Mary Landrieu of Louisiana, Kay Hagan of North Carolina, Max Baucus of Montana and Mark Pryor of Arkansas.
Also targeted by Bloomberg's ads are 10 Republican senators, including Jeff Flake of Arizona home of ex-Rep. Gabrielle Giffords, who was severely wounded in a mass shooting the retiring Saxby Chambliss of Georgia and moderate Susan Collins of Maine.
The Senate gun bill also would increase penalties for illegal gun sales and slightly boost aid for school safety.
White House spokesman Josh Earnest said Obama will travel to Denver Wednesday to talk to local leaders about Colorado's efforts to reduce gun violence.