White House considers responses to Connecticut shooting WASHINGTON - As gun control advocates cheered President Obama's call to action on gun violence, the White House began to weigh its options Monday on how to fulfill the president's vow to use all the power of his office to prevent future mass killings. The most likely initiatives following Friday's Connecticut school shooting - efforts to tighten gun show sales, for example, or to reinstate a ban on assault weapons - are laden with political pitfalls and challenges. Although several members of Congress indicated they were newly open to gun control measures, opposition to stiffer gun laws is expected to remain firm, particularly in the Republican-led House. Taking on another uphill legislative battle would scramble an already full agenda for the White House, which is embroiled in fiscal negotiations and hoping to start Obama's second term with a focus on immigration reform. Gun control supporters pushed the White House to move quickly to harness the anguish and outrage at the Newtown massacre, in which 20 first-graders and six adults died. But the president needs time to build consensus for any action in Congress, said an advisor who asked not to be named discussing strategy. Aides said the president wanted to avoid pushing gun partisans into their usual foxholes on an issue that has deeply entrenched and well-funded interests. White House spokesman Jay Carney declined to outline an agenda or offer policy specifics, although he said gun control measures would be under consideration. "I don't have a series of proposals to present to you," Carney told reporters. This is a complex issue that requires complex solutions, and he looks forward to engaging the American people in an effort to do more. Obama met at the White House on Monday with Vice President Joe Biden and senior staff members to consider ways to respond. Gen. Eric H. Holder Jr., Health and Human Services Secretary Kathleen Sebelius and Education Secretary Arne Duncan also took part. Experts say the president could take some steps to strengthen gun laws without congressional approval. For example, the law already forbids some mentally incompetent people and drug users from buying guns. But the administration could expand its use of government resources to improve the database used in background checks, or better fund efforts that help state and local agencies improve their databases. A string of previous tragedies sparked similar calls for stiffer gun laws, only to see pressure fade as politics and time eroded the sense of urgency. The Justice Department began an effort to research measures that would tighten gun laws and improve background checks, without banning weapons, after a gunman killed six people and wounded 13 others, including Rep. Gabrielle Giffords (D-Ariz.), in Tucson in 2011. Some of the changes did not require congressional action. Most have not been imposed. "My judgment is that if we're going to move, we need to move on them fairly expeditiously," said Christopher H. Schroeder, who researched the policies at the Office of Legal Policy before leaving the Justice Department this year. As horrific as the Connecticut shooting was, memories tend to fade. There's a limited window of opportunity to act. In an emotional speech Sunday night in Newtown, Obama raised expectations of direct engagement when he promised to use "whatever power this office holds" to prevent similar mass killings. He did not mention the words "gun" or "weapon" in his speech, or offer specifics. It was the fourth time Obama had addressed the nation to express grief after a monstrous crime. He wiped away a tear as he spoke, two days after a poignant White House appearance in which he repeatedly dabbed his eyes and fought to maintain composure as he decried the school massacre. Some signs indicated the Newtown killings could weaken opposition to new gun laws in Congress. Two prominent Democrats - Sens. Joe Manchin III of West Virginia and Mark R. Warner of Virginia - said Monday that despite their history of defending gun rights, they now believed tighter laws were needed. Manchin, whose candidacy was endorsed by the National Rifle Assn., said the Newtown shooting "has changed us." "Everything should be on the table," said Manchin, who in a 2010 campaign TV ad fired a rifle at one of Obama's legislative proposals. We need to move beyond dialogue - we need to take a sensible, reasonable approach to the issue of mass violence. Polls often find support for tighter gun laws evenly divided, but a survey released Monday suggested a slight shift in favor of gun control.