“The real challenge,” Ms. Mills wrote, “is that this likely will be when people want experience and we got so burned by that narrative” in the 2008 campaign against Barack Obama that “we won’t go back to it, even though it might be right for now.”

Emails reveal the care advisers took with every part of the campaign — right down to a single Twitter post.

The emails reveal the excruciating decision-making behind every step related to how Mrs. Clinton handled everything from her splashy campaign rollout speech on Roosevelt Island in June 2015 to a single Twitter post.

In one email chain from March 2015, four aides debated a Twitter post in which Mrs. Clinton would address for the first time revelations that she had used a private email server during her tenure at the State Department. “I want the public to see my email. I asked State to release them. They said they will review them for release as soon as possible,” the post eventually read.

That included their delight at an early ‘ad-libbing’ approach and jabs at President Obama.

“She smacked down POTUS on trade and kept kicking for a little bit,” Huma Abedin, a close aide, wrote on June 14, 2015, using an acronym for the president. “Worth looking at the transcript but this seemed to really work for this crowd.”

At the time, Mrs. Clinton was trying to craft herself as more of a populist, pointing to differences between her and Mr. Obama.

The aides also liked the personal details she shared. “She inserted some new applause lines and talked about Dorothy,” her mother, “in a more personal way that I’ve only heard talk about privately,” Ms. Abedin wrote.

Other emails show the anxiety that her team felt over making her opposition to the Keystone XL oil pipeline public.

Aides discussed leaking it after a meeting with labor leaders — so as not to undermine her “principled stand about not second-guessing the president in public.” Mr. Mook suggested that Mrs. Clinton time her announcement to “help distract” from the barrage of criticism surrounding her use of a private email server.