It’s been less than a year since President Obama recruited as his chief of staff Bill Daley, an accomplished man with business credentials and a polished private-sector résumé. Obama elevated Daley just days after the Tucson shooting, which gripped the nation and demanded the president’s leadership. And it was after his first chief of staff, Rahm Emanuel, went back to local politics in Chicago and Emanuel's replacement, Pete Rouse, expressed discomfort in the high-profile job.

So it took Washington by surprise Monday that Daley wouldn’t make it to his first anniversary in the West Wing’s corner office.

A White House staffer points to several reasons why Daley offered his resignation letter in the Oval Office last week. There’s the obvious fact that trust between Obama and Daley never quite grafted effectively, and that Daley’s corporate past ended up not winning the president any new favor with the business community. Daley himself pinned the reason on a classic Washingtonism: that he simply wanted to return to his hometown of Chicago and spend more time with his grandchildren.

But the timing of his departure points to a potential tipping point that over the course of last week has roiled the White House. The new book, The Obamas, by New York Times reporter Jodi Kantor, offered a frank portrait of the president and his wife, as well as how their aides work together. “Not well” has been the narrative that took hold after snippets of the book leaked last week. (It goes on sale Tuesday.) Kantor tells several unflattering vignettes suggesting pettiness and even resentment within the executive compound, and friction between senior aides and the first lady. Thirty-three aides, some past, some present, spoke to Kantor for the book, reflecting poorly on Daley’s ability to contain the West Wing's dirty laundry.

Kantor pieces together details from tense White House meetings, including one where former press secretary Robert Gibbs allegedly cursed Michelle Obama after hearing she was unhappy with a media scandal that he tried to avert. In another, Kantor drops the bombshell that Emanuel at one point offered Obama his resignation after a series of columns criticized Obama’s management style and glorified Rahm for holding the administration together. The White House has pushed back hard against the book, noting that Kantor never interviewed the first couple and maintaining that she overdramatized occasional disagreements among staff. Press Secretary Jay Carney said the Obama White House runs with remarkable efficiency compared with others he had seen. He declined to address specific anecdotes in the book.

In his resignation letter, obtained by The Daily Beast, Daley offers effusive praise for the president, enumerating his best-of album from the past year. “You have shown leadership … fighting for middle class … ending the war in Iraq … bringing Osama bin Laden to justice … passing Free Trade Agreements.” Offering no reason for his departure, he simply states that “it’s time for me to go.”

But in Washington, a city that loves a good personnel shakeup, the writing has been on the wall for Daley since the summer, when the economy entered an even deeper slump. Obama’s game of chicken with Congress over the debt ceiling proved that the White House’s relationship with legislators never actually improved. Both realities were a referendum on Daley’s inability to guide the administration’s tiller to allow Obama to focus on bigger-picture goals. That, in fact, was evident in November, when the White House announced that Daley’s role would be decreasing and Rouse would take on the daily duties of making the West Wing’s trains run on time. Despite the administration’s spin that it was just a routine shifting of responsibilities, it was viewed as a demotion for Daley.

While announcing Daley’s departure, Obama struck a personal tone, noting his chief of staff’s wise counsel, and his reluctance to accept Daley’s resignation. Yet he doesn’t have much time to dwell, or linger with a less-than-sleek staff. Over the next 10 months, Obama needs his team to work effectively to tout his accomplishments—and try to rack up a few more—before voters decide whether to rehire him in November.

In Daley’s place, Obama announced Monday afternoon that he’d elevate Jack Lew, the director of the Office of Management and Budget, to be his new chief of staff. Lew has been a member of Team Obama since the beginning of the administration, and has wide government experience. Having come to Washington as a Hill staffer in 1973, he has held nearly every Washington job: agency head, deputy secretary of state, special assistant to the president, think-tank scholar. He helped design the AmeriCorps program and has sat on the National Security Council. That résumé, combined with Lew’s unruffled cool and low-profile demeanor, hints at the kind of connected and disciplined leadership Obama thinks is important for the next, and potentially final, year of his administration.