WASHINGTON — In December 2009, toward the end of her first year as secretary of state, Hillary Rodham Clinton agreed to a joint interview with perhaps her best-known living predecessor, Henry Kissinger.

As she pondered the encounter, she began to worry that her distant relationship with President Obama, who beat her for their party’s presidential nomination, might contrast unfavorably with Mr. Kissinger’s close collaboration with President Richard M. Nixon.

“In thinking about the Kissinger interview, the only issue I think that might be raised is that I see POTUS at least once a week while K saw Nixon every day,” she wrote in an email to aides, using the acronym for the president of the United States. “Of course, if I were dealing w that POTUS I’d probably camp in his office to prevent him from doing something problematic,” she added cheekily before returning to the main point: “Do you see this as a problem?”

She evidently did, at least potentially, then went ahead with the interview. But her concern reflected the awkward marriage of former rivals at the start of the Obama presidency. The release this week of about 3,000 pages of emails from Mrs. Clinton’s first year at the State Department presents a rare glimpse into the daily life of a secretary of state — especially one whose tenure will be at the heart of a campaign to win the presidency, which eluded Mrs. Clinton seven years ago.