While Hillary Clinton continues to be seen as the frontrunner to become the Democratic Party's nominee for president, her campaign has been dogged by a months-long scandal involving her use of email during her time as secretary of state.
The controversy centers on Clinton's decision to use a personal email account on a privately maintained server rather than a State Department-issued system, which theoretically would have allowed for more thorough documentation of her official correspondence and better protection against hackers.
While Clinton has acknowledged that using the private email server was a "mistake," she insists her actions were legal. She says she only used a private email system for the sake of convenience, since she did not want to carry separate mobile devices for her work and personal communications.
Soon after the story broke in March, Clinton agreed to turn over 55,000 pages of work-related emails to the State Department to be made public. But she generated further controversy after it was revealed that she attempted to delete more than 30,000 other emails that her staff deemed to be "personal."
The matter has taken on increased political importance, and could continue to dominate the discussion around her presidential candidacy well into the future, since it is the focus of separate investigations by the Federal Bureau of Investigation and a Republican-led Congressional committee.
Breaking the law
One reason why the email scandal is significant is because federal law stipulates that "knowingly" removing or housing classified information at an "unauthorized location" is punishable by a fine or up to a year in jail.
But there are doubts such a criminal charge could stick, since Clinton has repeatedly said she never knowingly sent or received any information that was marked classified at the time it was sent or received. (Some of the information in the emails has been retroactively marked as classified by government inspectors evaluating the messages.)
There is also question whether Clinton's attempt to eliminate all personal emails from her server violated the Federal Records Act, which prevents government employees from destroying their official communications.
Clinton's lawyers insist that none of the then-secretary's personal correspondence sent or received via her private email server should be seen as federal records; her critics counter by saying it should not be up to Clinton or her staff to determine what is personal or official communications.
Critics have also accused Clinton of endangering national security by storing sensitive diplomatic intelligence on a homemade email server that lacked top-level security protection.
Hackers in China, South Korea, and Germany attempted several attacks on the server after Clinton left office in early 2013, according to a recent report by the Associated Press.
However, it is not clear how advanced the cyber intrusion attempts were or whether the attackers even knew they were targeting Clinton's emails. The report, which cited a congressional document, said the hacking attempts were blocked by an unspecified "threat monitoring" product.
Though the practice of using a private emails for official correspondence may seem unorthodox for top U.S. officials, Clinton's supporters have argued the practice is consistent with the way her predecessors conducted business.
Ex-Secretary of State Colin Powell also admitted to using a personal email account during his tenure as America's top diplomat, according to Politico.
The only other two former secretaries of state that have been in office since the advent of the email era — Condoleezza Rice and Madeleine Albright — say they did not frequently use email to conduct official business.
What the polls say
Clinton has lost about 20 percent of Democratic voter support since May, according to recent opinion polls, although it is impossible to know how big a role, if any, the email issue has played in those numbers.
As the scandal persists, Clinton has taken a more contrite stance. Last month, she offered her most frank statement of regret yet: "As I look back at it now, even though it was allowed, I should have used two accounts. That was a mistake. I’m sorry about that. I take responsibility," she told ABC News.
But there few signs the issue will go away anytime soon. This is especially due to its slow-drip nature: the State Department so far has only publicly released 37 percent of the Clinton emails. The outcome of the FBI investigation is also still pending.