Vice President Joe Biden gestures as he addresses at the U.S. Conference of Mayors 81st winter meeting in Washington on Thursday. (Manuel Balce Ceneta/AP)

One day after President Obama unveiled his far-reaching proposal for gun-policy reform at an emotional White House news conference, Vice President Biden renewed the administration’s call for action, telling a summit of the nation’s mayors that the issue is “more urgent and immediate” than any other facing the country.

Speaking Thursday at the winter meeting of the U.S. Conference of Mayors, Biden devoted the entirety of his remarks to delivering a point-by-point defense of the White House gun agenda that he helped to spearhead, using stark, often personal language.

“I know we don’t have absolute unanimity in this ballroom — nor do we in any ballroom — but we all know, everyone acknowledges we have to do something,” Biden told the crowd of mayors gathered at a Hilton hotel down the street from the White House. “We have to act. And I hope we all agree that there’s a need to respond to the carnage on our streets and in our schools.

“I hope we all agree that mass shootings like the ones that we witnessed in Newtown 34 days ago cannot continue to be tolerated,” he added, calling the tragedy one that “in all my years in public life, I think, has affected the public psyche in a way that I’ve never seen before.”

Since being tapped last month to serve as the Obama administration’s point man on gun policy reform in the wake of the Newtown, Conn., elementary school shooting, Biden has met with more than 200 groups representing a range of stakeholders on the issue.

President Obama proposed expansive gun-control policies aimed at curbing gun violence. The Obama administration can implement about half of the proposals, but the others — arguably some of the more critical initiatives — will require congressional approval.

He told the mayors that “no group was more consequential or instrumental in the shaping of the document we put together for the president than all of you in this room.”

In the response, however, there were early signs of the political difficulty the White House faces in pressing Congress to move forward on gun-control legislation.

The mayors and others in the ballroom applauded several times throughout Biden’s speech, including when the vice president called for universal background checks and argued that high capacity magazines “aren’t worth the risk.” They also cheered Biden’s call for increased funding for local law-enforcement efforts and the mental-health provisions of the Obama administration’s new plan.

But the applause was not universal, and the crowd responded with silence for much of Biden’s nearly hour-long address.

The vice president acknowledged that the White House is likely to come under criticism for many of its gun proposals, both from opponents of the provisions as well as from supporters who are questioning why the administration has not moved with similar urgency on other policy matters, such as immigration reform.

“Look, folks,” Biden said, addressing those critics. “Presidents don’t get to choose what they deal with. They deal with what is before them, and then what they’d like to long-term.”

He also pledged that the horror of what transpired in Newtown means that “this time will not be like times that have come before.”

“Newtown has shocked the nation,” he said. “The carnage of our streets is no longer able to be ignored. We’re going to take this fight to the halls of Congress. We’re going to take it beyond that. We’re going to take it to the American people.”

As Obama did at Wednesday’s White House news conference, Biden on Thursday made an emotional appeal for action, describing to the mayors “the image of first-graders not only shot, but riddled with bullets; parents in the streets panicking, trying to find out if the child they put on the bus in the morning had any prospect of getting back on that bus and going home that afternoon.”

“For 20 of those parents, the answer was no,” he said.

He told the group that the issue facing the country post-Newtown “isn’t just about guns — it’s about the coarsening of our culture.”

“It’s a very complex problem. And it requires a complex solution,” Biden said.

Not present among the mayors at Thursday’s event was New York Mayor Michael R. Bloomberg (I), one of the nation’s most vocal gun-control advocates.

In his opening remarks before Biden took the stage, Philadelphia Mayor Michael Nutter (D), the president of the mayors’ group and a staunch ally of the White House, defended the administration’s action and told those in the ballroom that “we can and we must act to help protect the lives of those in the future.”

“This has nothing to do with taking guns away from those who lawfully own them,” Nutter said. “Mayors respect Second Amendment rights and the legitimate use of firearms. But your right to use a firearm should not interfere with my right to live.”

The White House’s gun-control push comes as some Democratic governors across the country — including a few considering presidential bids — are moving forward with their own agendas on an issue that could well play a role in the party’s 2016 primary race. Among those governors are Maryland’s Martin O’Malley, Massachusetts’s Deval L. Patrick and New York’s Andrew M. Cuomo. Biden notably has not closed the door to a bid of his own.

Some of the mayors who listened to Biden speak Thursday said they believed that while it is early in the process, the gun issue could be a defining one in the next battle for the White House.

“My hope is that we get some of these [gun measures] through and that when 2016 comes around, those who are competing for office will say, ‘I did the right thing, and because I did the right thing, this nation is better off,’ ” said Michael B. Coleman, who for 13 years has served as the Democratic mayor of Columbus, Ohio.

“I think those who stand in the way of reform are going to find themselves in 2016 in trouble, because I think the public’s had it,” he added.