WASHINGTON — In the hours after the San Bernardino rampage, President Barack Obama reiterated the plea for "common sense gun safety laws" that he has made after virtually every mass shooting during his presidency.
But top White House advisers say they are still struggling to find a way for Obama to use his executive powers and tighten restrictions on gun sales, sidestepping a gridlocked Congress. While he has ordered officials to find ways for him to act unilaterally, aides said they have run into legal and political hurdles that make that difficult.
"This policy-making process involves consideration of complex policy, legal and operational considerations, and the president's team wants to make sure that everything we do in this area makes good common sense, is on strong legal footing, and can be effectively implemented," said Eric Schultz, a White House spokesman. "This work is very much under way."
The White House has focused its deliberations on an executive action that would detail who should be considered a high-volume gun dealer, a move that could expand background checks to a huge number of sales at gun shows, online, and elsewhere that now fall outside the law.
But taking that step would also open Obama to new charges that he is abusing his authority, even as the Supreme Court considers whether to review the legality of his actions to provide work permits and protection from deportation to 5 million undocumented immigrants.
While some gun control advocates had hoped to see Obama announce new rules on Dec. 14, the anniversary of the 2012 school shootings in Newtown, Conn., there is virtually no chance of that happening. With White House lawyers still poring over the legal questions, officials said any announcement would be at least a month away.
Valerie Jarrett and other White House advisers have held a series of meetings in recent weeks with gun control advocates who are pushing for Obama to take strong executive action in the absence of any legislation from Congress. Among those who have attended the meetings is Gabrielle Giffords, the former Arizona congresswoman who was shot in the head during a mass shooting in 2011.
Her husband, Mark Kelly, said he thinks spelling out the definition for a gun dealer would help catch some of the improper sales that are done off the books at gun shows. He said he spoke with the president about that idea early this year. "I'm optimistic that they will do something to improve the system," Kelly said in an interview.
At the same time, opponents of any unilateral action by the president are preparing to mount political challenges and to file lawsuits if he acts on his own, without congressional involvement.
"We stand ready to fight any backdoor attempts at gun control from the president," said Jennifer Baker, a spokeswoman for the National Rifle Association's lobbying arm, which has been monitoring the White House deliberations. "As he gets closer to the end of his term, he's becoming more desperate to deliver a victory for gun control by executive fiat."
His advisers believe that by defining the number of gun sales or other factors needed to qualify as a "high-volume" dealer, Obama could greatly increase the number of sales subject to such screenings, weeding out more of those barred from buying guns because of criminal offenses, domestic abuse or mental health issues.
Other steps under consideration by the president's aides include broadening a provision that bars domestic abusers from buying guns, as well as giving the FBI more time to run background checks. Taken together, the steps could require background checks for hundreds of thousands of additional gun sales.
But the aides acknowledged in interviews that using the president's executive authority to take these steps would pose a complex set of obstacles. For instance, changing the definition of "gun dealer" is more complicated than simply lowering the threshold for how many gun sales are required to be considered a high-volume dealer.
White House officials said it is highly unlikely that Congress would be willing to finance the additional costs of enforcing the new definition or pay for additional background checks, which are conducted by federal law enforcement agencies.
In addition, officials said there was almost no accurate data about how many gun sales are made at gun shows or online by people who are not considered high-volume dealers. That makes it difficult to know how many people would be affected if Obama takes action to reinterpret the law.
Even so, gun control advocates who have met with the White House say they are optimistic that Obama will move ahead with at least some of the steps under discussion.
"I think they've arrived at a place where they're committed to a set of executive orders," said Pia Carusone, executive director of Americans for Responsible Solutions, the gun control group started by Giffords after her shooting. Carusone, who has attended several meetings with officials recently, said of Obama: "He doesn't want to leave the White House without doing anything on guns."
Officials said the president and his aides recognized that the Republican-controlled Congress was unlikely to pass any new gun measures before Obama leaves office. But on Thursday, Obama's spokesman insisted that the president remains committed to new gun laws if lawmakers would agree to pass them.
"I assure you that the president's passion for laws that would make it harder for individuals who shouldn't get guns from getting them has not waned," said Josh Earnest, the White House press secretary.
Earnest repeatedly sought to place the blame for inaction squarely on Congress. He suggested that lawmakers should pass a law prohibiting people from buying guns if they have been placed on the country's no-fly list of terrorism suspects.
"Republicans can't even explain why they actively oppose the passage of that law," Earnest said, adding: "The president is determined to do everything he possibly can to try to make our country safer. And he certainly believes that members of Congress should have the same impulse."