The operatives were joined by current administration staff and past presidential personnel to focus on a common goal: November 9 and beyond.
The presidential transition is one of the least public but most important parts of any presidential election. With only 72 days between Election Night and Inauguration Day, good governance experts and recent federal officials have been pushing for candidates to start planning a potential administration earlier and earlier in the election calendar.
Presidential transitions have always existed in some capacity, enshrined in law in the Presidential Transitions Act of 1963.
But while for years the efforts were privately funded and ad hoc, the federal government has been formally supporting transition operations since 2010.
For starters, a new White House has to fill approximately 4,000 government positions, including roughly 1,100 that require Senate confirmation. Most new administrations only manage to fill a few hundred in its early months, and only about 80% of the positions are full at any given time in an administration, on average.
In addition to the massive personnel undertaking, a transition has to figure out how to turn the candidate's campaign promises into actual policy.
A new president is also expected to deliver a budget request for the entire government in early February, and give a State of the Union (or similar) address, undertakings that cannot be completed without starting well ahead of Inauguration Day.
In 2012, the transition effort for Republican candidate Mitt Romney had upwards of 400 staffers who were organized into policy groups mimicking federal agencies, who were starting to draft a 200-day plan for a potential Romney administration.
Trump transition Chairman Chris Christie has told lobbyists and influencers in Washington meetings that their operation is reviewing executive orders and regulations to see what could be changed in the first 100 to 200 days of a new administration.
Why is it important?
The time in which the US government is handing over power is arguably the most vulnerable period in our democracy.
While some federal officials may be held over between administrations, even when parties change power, the vast majority of federal agencies -- covering homeland security to public health to the economy -- will be operating without permanent leadership in place or with brand new leaders.
The workforce made of non-appointee career officials will remain in place, but coordinating a response to an event that threatens the public can be hampered by principals from different agencies working together for the first time.
Transitions are encouraged to develop response plans for possible national emergencies -- be they health, weather, terrorism or other dangers -- and conduct table-top exercises to prepare.
"You don't want the president with his or her staff sitting in the Sit Room, doing it for real, when it's the very first time," said Clay Johnson III, the former transition executive director and White House official for President George W. Bush. "You can just imagine if 9/11 had been 2/11 or 1/21/11, how important it would have been to have a president and his national security people in place, really briefed, having had some at least prior exposure to the process and the other people they would be in that room with, if and when something awful like that happened."
So the transition starts before the election is over?
For years it was considered "measuring the drapes" to begin planning for a potential administration before the race was won, but it has become more accepted in recent years to begin well before votes are cast -- even before the nomination is secured.
With the amount of work a transition must do, the operation is seen as in the public's interest, even though one candidate will lose and the work will be for naught.
Barack Obama and John McCain were both encouraged to stand up transition operations formally before the election, and starting with the 2012 election, the government has provided resources to do so.
According to memoranda of understanding signed by representatives of Clinton and Trump with the General Services Administration, obtained by CNN through the Freedom of Information Act, federal office space was made available for both candidates' staffs starting August 1, 2016, after their formal nomination by the parties' conventions.
After the election is over and a winner is apparent, the loser must move out within five days and the victor will have two weeks to transition to space provided for the president-elect, according to the MOU.
Before the election, the transition remains largely separate from the campaign, so as not to distract from the primary goal of winning. Past transition leaders told CNN they provided periodic updates to the candidates, but largely stayed out of their hair.
While the transition will prepare a list of potential names for the top positions the president-elect will need to fill, vetting is kept to open source information so as not to tip off individuals to their consideration prematurely.
Still, preparations can advance significantly before the election. Emails hacked from the private account of Clinton's campaign Chairman John Podesta and posted by WikiLeaks date back to 2008 -- when Podesta chaired Obama's transition.
The emails reveal a humming operation before Election Day, increasingly confident in its chances.
On the afternoon of Election Day in 2008, Susan Rice emailed Obama's transition executive director Chris Lu about fielding calls from foreign leaders post-election.
"In anticipation of the many calls from foreign leaders, we have prepared a list of priority calls to return and the briefing memos," Rice wrote. "Our view is that he should return the calls through the State Dept. Ops center, which is comparatively apolitical and professional, has translation capabilities and can assist as desired with notetaking."
She added that someone from the team should contact State first thing Wednesday morning. Obama, of course, went on to win that night.
The Clinton campaign has declined to confirm or deny the authenticity of the emails being released every day in batches by WikiLeaks, blaming the Russian government for their release, which Moscow and WikiLeaks have denied.
Who pays for all this?
The transition is paid for by a combination of federal and private funds.
The GSA provides both the candidates 16,000 square feet of office space -- enough for 114 people -- before the election, along with office equipment, technology and furniture, according to the MOUs. They also provide security staffing and IT support within pre-established hours.
The GSA got more than $13 million for pre-election transition activities in the fiscal year 2016 budget.
To pay for staffing, presidential transitions are allowed to set up tax-exempt organizations to fundraise. Per GSA agreements, they are only allowed to accept $5,000 per person or organization and are required to disclose all donations by February 19, 2017.
Romney raised nearly $4 million for his transition team, as did Obama in 2008, though Christie has told potential donors that Trump wanted to run a leaner effort and that the target was closer to $2 million.
Though money has yet to be formally allocated by Congress, the requested budget for the incoming president's transition is $7 million -- $6 million for the president-elect and $1 million for appointee orientation, the MOUs say. But that money can only be used after the election.
Post-election, the GSA will continue to provide space and equipment, and the money can also be used for travel for employees or official guests -- for example inviting candidates to be interviewed or vetted for appointments. Past candidates for Cabinet positions often spent their own money to be interviewed.