NEARLY three years ago, in the days after the mass killings at Sandy Hook Elementary School, President Obama went to Newtown, Conn., to speak at a vigil for the victims. He spoke movingly, and seemed to embody the nation’s outrage and its determination to reduce the number of people killed with guns in America. “Do not lose heart,” he told the families of the victims. He said he would use “whatever power this office holds.”

He has not done that. He tried one lever of presidential power — proposing legislation. When that didn’t work, the president failed to move the other levers in a meaningful way.

For more than a year, we and fellow religious leaders across the nation have worked to persuade President Obama to use what we believe is the most powerful tool government has in this area: its purchasing power. The federal government is the nation’s top gun buyer. It purchases more than a quarter of the guns and ammunition sold legally in the United States. State and local law enforcement agencies also purchase a large share. Major gun manufacturers depend on these taxpayer-funded purchases. For the government to keep buying guns from these companies — purchases meant to ensure public safety — without making demands for change is to squander its leverage.

Some of the leading brands of handguns purchased by the government — Glock, Smith & Wesson, Sig Sauer, Beretta, Colt, Sturm, Ruger & Company — are also leading brands used in crimes. Among the brands of handguns recovered by the Chicago Police Department at crime scenes between January 2012 and October 2013, all six of these companies ranked in the top 11. When police officers carrying Glocks are recovering Glocks at crime scenes on a regular basis, shouldn’t this prompt questions about whether the police department could use its influence to reduce the number of guns that end up in the hands of criminals? When Smith & Wessons turn up frequently in the hands of criminals, shouldn’t questions be asked when Smith & Wesson seeks a contract with the federal government?