President Barack Obama pushed back Thursday against opponents of tighter gun laws, saying it would be "shame on us" if Washington fails to act after last year's mass shootings, like the one in Newton, Conn., that left 26 dead, 20 of them children.

"I haven’t forgotten those kids. Shame on us if we’ve forgotten," he said. "If there is one thing I’ve said consistently since I first ran for this office, nothing is more powerful than millions of voices calling for change."

Standing with Vice President Joe Biden and families affected by gun violence, Obama said it was Washington's "best chance in a decade" to strengthen gun laws. However, the president candidly acknowledged that the issue has lost some of its resonance and could be stonewalled into oblivion by considerable opposition.

Several recent polls have found a sharp drop in support for new gun laws. A CBS News survey released this week found that less than half of Americans now support such measures, down from the 57 percent who supported them shortly after the Sandy Hook shooting. At the same time, neither chamber of Congress has passed a gun bill this year, and a proposed ban on assault weapons — once a central element of the White House's plan for broader gun legislation — was scrapped by Senate Democrats for lack of support.

In his speech, Obama urged Congress to move ahead with other proposals still on the table, such as limits on magazine capacity and expanded background checks. "None of these are controversial," nor will they infringe on the Second Amendment, he insisted.

Yet those proposals are controversial, and have drawn considerable opposition from conservatives and the National Rifle Association.

A group of Republican senators has already vowed to filibuster gun bills in that chamber, and bipartisan negotiations over the very proposals Obama touted on Thursday fell apart earlier this month, with Republicans walking away entirely. If legislation ever advances to the Republican-controlled House, it would face an even tougher test there.

As for the NRA, they appeared to be flailing in December, but have since bounced back with two straight months of enormous fundraising and an arsenal of slick new ads. "Wayne LaPierre Is Winning," an editorial in The Nation lamented, referring to the NRA's CEO and executive vice president.

In once again publicly pressing for new gun laws — as he did immediately after the Newtown massacre and in his State of the Union speech — Obama is hoping to revive support and prevent his opponents from, as he said, "running out the clock." In the speech, which was timed to coincide with a national day of action on gun laws, he called on Americans to keep up the fight by contacting their representatives and pressuring them to act.

"We need everybody to remember how we felt 100 days ago and make sure that what we said at that time wasn’t just a bunch of platitudes, that we meant it," he said.

He'll take that message on the road next week; he's scheduled to be in Colorado to tout that state's new gun laws.