WASHINGTON — President Trump’s plan to move the Secret Service from the Department of Homeland Security back to the Treasury Department risks unraveling the cabinet agency responsible for securing the United States, according to a report issued by a group of government officials formed to study the move.
Since last year, Treasury Secretary Steven Mnuchin has discussed taking control of the Secret Service with White House officials and, in recent weeks, members of Congress. James M. Murray, the Secret Service director, also recommended moving the agency back to Treasury, where it was housed until 2003, when the Department of Homeland Security was founded after the Sept. 11, 2001, attacks.
Officials from both agencies believe the move could improve investigations into financial crimes and provide more support for the Secret Service, since the Homeland Security Department under Mr. Trump has been increasingly focused on immigration.
But a working group of homeland security, Treasury and White House officials formed last year to examine the issue said that homeland security officials and lawmakers could “perceive” the “loss of the Secret Service” as leaving behind a “weakened D.H.S.”
“Such a loss could open D.H.S. up to additional reforms or reorganizations, perhaps even some involving the transfer or dismantling of other operating components, further weakening the department at a critical time in its development,” according to the report obtained by The New York Times.
The group said the administration must develop a plan to support the other agencies in the homeland security department.
The move could also hurt the department’s efforts to protect the nation from threats to its computer networks, the group said in the report. In addition to protecting the president and his family, the Secret Service is also responsible for investigating financial crimes and currency counterfeiting.
The White House is planning to formally propose the move in its 2021 budget, which is expected to be released next month.
Recently, Mr. Mnuchin has been actively lobbying the Republicans and Democrats in Congress to backing legislation needed to make the move. The effort hit a snag last year when Senator Dianne Feinstein of California, the top Democrat on the Judiciary Committee, began pressing the Secret Service to produce reports detailing the cost of protecting the president, according to people familiar with the matter.
Mr. Mnuchin supported the idea of such reports, but insisted that they not be released until after the 2020 election, these people said. The Trump administration was wary that such reports could give his opponents ammunition to criticize him for the exorbitant costs of his travel to his Mar-a-Lago estate in Florida and to his golf clubs, hotels and other resorts.
Two administration officials said Ms. Feinstein had recently warmed to receiving the reports in December. A spokesman for Ms. Feinstein’s office said negotiations with the administration were continuing.
The Department of Homeland Security did not return requests for comment. Catherine Milhoan, a spokeswoman for the Secret Service, said in a statement the agency “has been involved in discussions regarding the potential move and is appreciative of the active interest in advancing its integrated mission.”
The Washington Post reported this month about Mr. Mnuchin’s opposition to releasing the reports before the election.
The Trump administration had hoped that legislation for the move could have been attached to a year-end spending bill last year, since it is not clear that there would be sufficient congressional support for a stand-alone bill this year — particularly without details on the costs associated with protecting Mr. Trump and his family.
“In the absence of getting that information you can only surmise that something must be amiss,” said Representative Bennie Thompson of Mississippi, the chairman of the House Homeland Security Committee, “or at least you’re trying to keep certain information away from members of congress.”
Mr. Thompson said he opposed moving the Secret Service because it could harm national security.
The creation of the Homeland Security Department after the Sept. 11 attacks reorganized multiple government agencies and moved agencies with security functions, including the Secret Service, under one umbrella. The department also includes the Coast Guard, the Transportation Security Administration, and agencies responsible for immigration, border duties, hurricane relief and cybersecurity.
While some senior officials at the Department of Homeland Security have expressed concern about losing an agency with those investigative components, high-ranking Secret Service agents have long felt neglected by the department. The Secret Service represents only 3 percent of the budget of the Department of Homeland Security, an agency that now has its fifth leader under the Trump administration, Chad Wolf, an acting chief who has yet to be nominated for the secretary position.
The Homeland Security Department and its many agencies have become frequent targets of critics of Mr. Trump’s immigration agenda. Democratic presidential candidates have proposed overhauling the department’s border agency, and some Democrats have pushed for abolishing Immigration and Customs Enforcement.
The working group also considered breaking up the Secret Service, according to the report, and sending the investigative branch to Treasury while keeping the protective arm at the Homeland Security Department. Another proposal involved moving one branch of the Secret Service to Treasury and the protective function to the Justice Department.
But agents have long held that the responsibilities are intertwined and splitting the agency would result in a lack of resources for the service. Officials in both Treasury and the Secret Service are eager to move the Secret Service in its entirety, according to the report.
Mr. Mnuchin’s fondness for the Secret Service has grown as he has bonded with his personal detail of agents, who often accompany him to SoulCycle sessions and on long bike rides from his mansion to Mount Vernon, according to people familiar with his exercise regimen.