In fact, the 36-year-old was already on the job -- almost three years before the vote.
"You are right about a long term press strategy. Need a different voice responding to this stuff," Mook wrote to Cheryl Mills, Clinton's longtime aide, in February 2014.
Mook's message was among the thousands of gmail messages hacked from the account of John Podesta, Clinton's campaign chairman, and released in recent days by WikiLeaks.
The Clinton campaign say the hack was carried out by Russian cyber spies bent on tilting the race in favor of the Republican candidate.
But the emails offer a fascinating window into the development of a presidential campaign that has been years in the making, with a tiny group of insiders working in secret to prepare Clinton's bid to become the first woman president of the United States.
The emails show that the candidate and her closest collaborators were determined not to repeat the errors of Clinton's unsuccessful presidential bid in 2008, when she lost to a charismatic newcomer, Barack Obama.
The former secretary of state let speculation build about her possible run for the White House, coyly deflecting questions about her future plans by saying she was enjoying time with her granddaughter.
Nevertheless, the press was already alert to signs of a Clinton candidacy. Mook's message about press strategy was prompted by a news story that examined growing differences between Clinton's camp and Obama's inner circle.
By March 22, 2014, Mook was starting to work on a campaign strategy, the emails show. He urged Clinton not to run for the presidency, as she had in 2008, as a woman seeking to make history, warning that would be a "mistake."
Instead, Mook argued, Clinton should run as a champion of the middle class -- a line she would embrace about a year later.
At the time, Clinton was busy shuttling from paid speaking engagement to paid speaking engagement, and readying a promotional tour for her memoir as secretary of state -- nothing that would suggest any direct political agenda.
But in April 2014, Mook already was thinking about how Clinton's campaign should be set up and where.
"I anticipate that about two dozen staff will need to be in place and working six to eight weeks prior to an official campaign announcement," he wrote. But he said they should not act before November 4, 2014 midterm elections.
In May 2014, Hillary Clinton was summoning her closest advisers. Even they were unaware that Mook was hard at work behind the scenes.
"The only person in this group that knows about you besides me is John," Mills wrote Mook, presumably referring to Podesta.
- Influencing the media -
In late 2014, as Clinton campaigned for fellow Democrats in congressional elections, her speechwriter Dan Schwerin worked up a 20-page document on possible "narratives" for her campaign strategy.
"The goal is for you to begin crystalizing the ideas and motivations that are most important and compelling to you, which will then provide direction for policy development, midterms messaging, and further research," he wrote.
One suggestion was: "I'm running for president to restore America's fundamental bargain with the middle class and get government working for everyone again, not just a wealthy few."
Another was "I'm running for President to renew the American Dream."
And "That's why we need a fighter in the White House."
Then the pace of hiring picked up. "Madame Secretary, Congratulations -- you have a very enthusiastic Communications Director and Deputy Communications Director," Mook messaged Clinton in January 2015, referring to Jennifer Palmieri and Kristina Schake.
The press strategy also had begun to take shape.
"We are all in agreement that the time is right to place a story with a friendly journalist in the coming days that positions us a little more transparently while achieving the above goals," wrote Nick Merrill, formerly at State, in a memo.
Focus groups were set up in New Hampshire in January 2015 to start fleshing out the campaign messages, but Clinton's pollsters found a problem after one messaging test.
"For an audience of core supporters, the enthusiasm is somewhat muted and we don't appear to be generating the excitement or a sense of a fresh, new candidacy we had hoped for," wrote pollster Joel Benenson.
A week before the campaign launch, daily calls were being held to coordinate strategy. Emails piled up in Podesta's mailbox as the April 12, 2015 launch date loomed.
Just one day before, Podesta and others spoke on condition of anonymity to at least one influential journalist.
Then, on the big day, Clinton sent this message on Twitter: "I'm running for president. Everyday Americans need a champion, and I want to be that champion. –H"
The "H" was intended to mean that the tweet was from her personally. But it was pre-written, and pre-approved at the highest level, at least a week before.
