WASHINGTON — The Trump White House instructed senior government leaders Monday to block cooperation with President-elect Joe Biden’s transition team, escalating a standoff that threatens to impede the transfer of power and prompting the Biden team to consider legal action.

Officials at agencies across the government who had prepared briefing books and carved out office space for the incoming Biden team to use as soon as this week were told instead that the transition would not be recognized until the Democrat’s election was confirmed by the General Services Administration, the low-profile agency that officially starts the transition.

While media outlets on Saturday projected Biden as the winner, President Trump has not conceded the election.

“We have been told: Ignore the media, wait for it to be official from the government,” said a senior administration official, speaking on the condition of anonymity because the person was not authorized to speak publicly.

The GSA, the government’s real estate arm, remained for a third day the proxy in the battle. Administrator Emily Murphy, a Trump political appointee who has lasted a full term in an administration where turnover has been the norm, is refusing to sign paperwork that releases Biden’s $6.3 million share of nearly $10 million in transition resources and gives his team access to agency officials and information.

In an indication of growing frustration among Biden transition officials, they organized a call with reporters Monday night to lay out some of the government services that Murphy’s decision is denying them. Those include State Department-facilitated calls with foreign leaders and access to secure facilities where they can review classified information.

The team is evaluating its legal options and growing increasingly alarmed that the stalemate could drag on and impede its work. The campaign has prepared for weeks for the possibility that Trump would not move forward with a peaceful transfer of power.

Still, with acutely high stakes for Biden during one of the most volatile periods in American history – with a weak economy and a government preparing for the daunting task of distributing a coronavirus vaccine – a shadow transition is beginning to take shape. Democrats have been out of power for just four years, and the Biden team is starting to reach out to its many contacts in and out of government, according to transition and former government officials.

On Monday many agencies, from the U.S. Agency for International Development to Veterans Affairs, took legal cover from Murphy’s decision to hold off on “ascertaining” an election winner. Political appointees have told their staffers, including career civil servants, not to respond to outreach from the Biden team, if there is any. No formal briefings on agencies’ projects, budgets, trouble spots or day-to-day operations – crucial building blocks that help an administration form a new government – are taking place.

The top political appointee at USAID, which provides billions of dollars in humanitarian assistance to foreign countries, told his staff that the agency would not cooperate with the transition until Murphy signed off.

John Barsa, acting deputy administrator, told colleagues that Biden had not won the election, emphasizing the importance of not abetting the transition process, two people familiar with his conversations said. A 440-page briefing book for the next president’s team sits ready and waiting at the agency.

“The only official announcement about an election result that matters is from the head of GSA,” Barsa said, according to a recording of a call published by the Washington Free Beacon, a conservative website.

Elsewhere in the government, months of preparation by career officials to relay information to the incoming team hung in limbo, and some senior staffers had received no communications from top leaders at their agencies.

“There is a process underway that is guided by law, and we will await conclusion of that process,” a VA spokeswoman said. At the Environmental Protection Agency, a spokesman said transition planning would be “inappropriate for us to discuss as votes are still being counted” and referred questions to the GSA. The Office of Management and Budget was “not transitioning” as of Monday, an official there said.

The career staff in the sprawling VA system was putting the final touches on a voluminous set of briefing documents for the Biden team, though, covering policies on private health care, coronavirus protocols and a massive electronic health records project, among hundreds of others, officials familiar with the planning said.

The refusal to carry out a tradition that has taken place immediately after most elections has quickly become another flash point in a divided country. Democrats on Capitol Hill condemned Trump for undermining a smooth transition of power and demanded that Murphy release $9.9 million in taxpayer-funded transition funding, which can be used to hire staff and buy equipment.

Republicans defended the president’s right to recount or question votes in battleground states that have been called for Biden. They settled on the contested 2000 race between Democrat Al Gore and Republican George W. Bush as their North Star, pointing out that the GSA chief appointed by Bill Clinton waited for a resolution before passing the transition torch.

The Biden campaign said it is holding out hope for a few days that Murphy and her White House allies will change their minds, and turned its focus early this week to filling top White House jobs such as chief of staff and naming a task force to amp up the government’s coronavirus response.

“There are things a transition is made better by cooperation, but it’s not absolutely dependent upon it,” said Michael Leavitt, a former Utah governor and health and human services secretary who planned the potential transition for Mitt Romney in 2012 and later worked to reform the law governing transitions.

The Presidential Transition Act, passed by Congress in 1963, does not specify what factors the GSA administrator must consider when determining the apparent winner of an election, giving Murphy leeway to make that call, experts on presidential transitions said.

But a legal challenge from Biden could be aimed at her authority to ascertain the results and make an independent judgment when she is taking instruction from a president who has a vested stake in the election. Not moving forward, Biden officials argue, could have national security implications because the incoming administration would be ill-equipped to handle current threats facing the country.

With formal transition resources out of reach at the moment, Biden officials are informally talking to people in and out of government to understand what lies ahead at federal agencies.

A senior member of the Biden transition team said members have drawn up a contingency plan in case the Trump administration refuses to engage with the Biden representatives. As part of the plan, the Biden team has made lists of recently departed senior officials at key agencies who are well-versed in issues facing various corners of the government – and could help incoming officials get up to speed.

The woman at the center of the transition storm, meanwhile, has continued to do her job and remains unflappable, said a senior administration official. Murphy has reached out several times for guidance in recent days to Clinton’s GSA administrator, Democrat David Barram, who awaited the results of the Florida recount and Supreme Court ruling in 2000 before handing off transition resources.

“It’s the closest situation to what we have now,” the official said. “Emily is following the law, and she’s following precedent.”

Murphy and her allies are pushing back on Democrats’ claims that the Trump administration had political motives when it installed a new general counsel at the GSA five days before the election.

Trent Benishek had been a special assistant in the Office of White House Counsel and was dispatched to the GSA soon after the agency’s previous chief attorney left to pursue a job in the private sector. Benishek now oversees 137 lawyers and, as the chief legal adviser, is likely to be in the middle of decisions about the transition.

The senior administration official described his hiring as “a normal move” and a career opportunity with more responsibility and higher pay.

At the same time, the Trump administration is using the transition to part ways with some appointees whose loyalty it has questioned. Defense Secretary Mark Esper was fired Monday. Last week, as votes were being counted, the head of the Federal Energy Regulatory Commission was stripped of his leadership post, and the No. 2 official at USAID was forced out. John McEntee, director of the Presidential Personnel Office, has told political appointees that they will be fired if they are caught looking for jobs, according to an administration official familiar with his conversations.

The Biden effort is being overseen by Ted Kaufman, one of his closest and longest-serving advisers. Kaufman also helped co-write an update to the law governing transitions, which was passed in 2015 and signed by President Barack Obama. While that law was aimed at smoothing the transition process by requiring both presidential candidates to begin preparations after their party conventions, it did not envision a conflict in which the GSA administrator refused to declare the winner.

After the contested election in 2000, it took until Dec. 12 for the Bush administration to begin the transition process, without access to many federal government resources. The administration’s sluggish start and lack of qualified personnel in place was cited by the 9/11 Commission report as a critical vulnerability to U.S. national security that prompted reforms to the law.

Biden’s transition team has been given government-issued computers and iPhones for conducting secure communications, for example, and has been granted 10,000 square feet of office space in the Herbert C. Hoover Building in Washington, although most of the work is being done remotely because of the coronavirus pandemic. His advisers have also been granted temporary security clearances and undergone FBI background checks to fast-track the processing of personnel who can receive intelligence briefings.

If the process doesn’t move forward, the Biden team won’t have access to the transition funds. But it is allowed under the law to accept donations of up to $5,000 from any person or organization.

Those donations must be disclosed within 30 days after the inauguration. Biden’s transition team declined to say whether it has started raising those funds or from whom.