WASHINGTON - President Obama pressed Congress on Thursday not to forget the heartbreak of the Newtown elementary school massacre and "get squishy" on tightened gun laws.
But some lawmakers in his own Democratic Party remain a tough sell on an approaching Senate vote to expand background checks on buyers.
"Shame on us if we've forgotten," Obama said at the White House, standing amid 21 mothers who have lost children to shootings. "I haven't forgotten those kids."
More than three months after 20 first-graders and six staffers were killed in Newtown, Conn., Obama urged the nation to pressure lawmakers to back what he called the best chance in more than a decade to tame firearms violence.
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 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 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 circumvent too easily.
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 after the Newtown killings.