What's Next in Hillary Clinton Email Investigation and What's at Stake As the FBI investigation winds down, what it means for the Clinton campaign.

 -- Late last week, sources confirmed the FBI had just finished interviewing a handful of former Secretary of State Hillary Clinton’s closest aides and advisers as part of an inquiry tied to her private email server, and that next it plans to ask Clinton herself for an interview, suggesting the review is nearing or entering its final stages.

Aside from defeating Donald Trump, it may be fair to say that this outstanding investigation about the handling of sensitive information on a private email server during her time at the State Department is the biggest obstacle on her path to the presidency. To clear that hurdle, the Justice Department must be convinced there was no criminal wrongdoing on her part.

As the FBI closes in on its decision, here's a look back at what got her to this point and what’s at stake going forward.

What Got Her Here?

Just days before she took office as secretary of state in 2009, Hillary Clinton set up her “clintonemail.com” domain for her and her top aide, Huma Abedin. After using the account for about two months, she moved it to a private server used by her husband Bill Clinton, run out their basement in Chappaqua, New York. She used that account exclusively throughout her time in office, never using a government address.

The account came to light as a result of the House select committee investigating the 2012 Benghazi attack and was then catapulted into public view when the New York Times reported on it on March 2, 2015. Clinton turned over about 52,000 pages of her emails, after deleting 30,000 messages she said were private in nature. News organizations sued the State Department under freedom of information laws, seeking the emails, and a judge ruled that the State Department must make them public.

As the emails were slowly produced, the inspector general for the intelligence community believed there was enough cause to ask the FBI to investigate whether classified information was mishandled via that account. The State Department later said that 22 of her emails couldn’t be published because they contained top secret information. And a Washington Post analysis of the final production counts 104 emails she personally wrote that were deemed classified.

Where Does the Investigation Stand?

The FBI will be interviewing Clinton in the coming days, meaning the investigation may be nearing a conclusion about whether to levy any criminal indictments. Law enforcement sources tell ABC News that so far they are not aware of any evidence indicating criminal wrongdoing.

The FBI's upcoming interview with Clinton, who is well coached on the issue, is unlikely to change that. Her campaign has long maintained she never mishandled sensitive material and said recently it is “confident the review will conclude that nothing inappropriate took place."

But the FBI was able to recover many of the emails that Clinton herself deleted, and it hasn’t said if anything new or incriminating might have been gleaned from those files. And her top IT staffer, Bryan Pagliano, has been offered immunity by the Justice Department and is said to be cooperating with the investigation. He might have insight into some of the more critical questions, such as whether the intent of the private server was to hide information from the public and if it was ever hacked by foreign entities.

What's at Stake?

At stake is the fate of Clinton’s presidential campaign. It’s more than plausible that a criminal indictment, however unlikely, would derail her bid and force the Democratic party to put someone else on the ticket. And if Clinton were to be indicted for sending classified information over a private email server outside of government control, some might argue that other secretaries of state should face similar charges.

The State Department’s inspector general concluded two months ago that Secretary Colin Powell and aides to Secretary Condoleeza Rice handled classified information on private email accounts. At the time, both secretaries made arguments similar to those of Secretary Clinton -- that the information was being over classified.

Editors Note: Originally this story incorrectly stated that Hillary Clinton's aide Cheryl Mills also had an account on that private server. On Oct. 17, 2016 this story was corrected to state that it was only her aide Huma Abedin who also had an address there.