A SENSE OF URGENCY is the most ephemeral thing in politics. That’s why the debate over gun control is reaching a key moment. The opportunity to do something serious about gun violence must not be lost. Vice President Biden, heading up the task force created after the Newtown, Conn., school massacre, kept the issue alive this week in a series of high-profile meetings with interested groups, from victims of gun violence to the National Rifle Association. The next step is to move from talk to action.

The Biden group is considering measures that would be broad and comprehensive, going well beyond reinstating the expired assault-weapons ban, including: universal background checks for firearms buyers; tracking the movement and sale of weapons through a national database; strengthening mental-health checks; and stiffening penalties for carrying guns near schools or giving them to minors. The vice president also raised the possibility that the White House could implement some measures by executive order, without legislation; a list of recommendations was drawn up in 2011 by the Justice Department but put on ice during the presidential campaign.

The working group is right to think big, yet it must be cognizant that legislation will face stiff opposition from the National Rifle Association. In today’s polarized environment, an omnibus bill might offer everyone something to oppose. It would be a mistake to ask Congress for a package so big that it sinks.

We support reinstatement of the expired ban on sales of new assault weapons and limits on high-capacity ammunition clips. These military weapons have no place in civilian hands. But this is not a whole strategy. The use of assault weapons in mass killings is horrific, but they are used in only a fraction of the nation’s deaths from gun violence. And any ban on new-weapons sales would not address the millions of assault weapons in private hands.

The White House would be wise to consider at least two other measures that polls suggest enjoy public support. One would be to require universal background checks for gun sales, closing a loophole in which more than 40 percent of sales, and perhaps up to half, are not subject to such checks, including through the Internet and at gun shows. The other would be federal legislation to tighten the definitions and penalties for gun trafficking, a problem that plagues the border with Mexico.

Beyond these, the White House can show leadership on the related issues of mental health and of violence in entertainment and video games. But the urgency of action, and the deep polarization of our politics, means the administration should choose its legislative priorities carefully, aiming for those with broad public support and a reasonable chance of approval. As Mr. Biden vowed the other day, “We are not going to get caught up in the notion that unless we can do everything, we’re going to do nothing. It’s critically important that we act.”