PHILADELPHIA -- The Democratic National Convention was sent into upheaval over the weekend when Wikileaks released nearly 20,000 internal emails from the party -- some of which showed officials working against Sen. Bernie Sanders in the primary.
US officials suspect the email dump is the work of Russian hackers who were discovered in DNC servers earlier this year, and experts believe the coordinated release of the documents on the eve of the convention are an effort by Moscow to meddle in the US presidential election.
Here's what you need to know about the leak.
How do we know this is the work of Russia?
Cybersecurity experts who initially responded to the DNC hack identified two distinct groups of hackers operating in the system -- one who had exclusively gone after the party's opposition research file on Donald Trump, and one that had been snooping on DNC emails for about a year.
Both were recognized as known Russian military or intelligence-affiliated hacking operations. Crowdstrike, the firm that responded to the hack, tracks dozens of advanced cyberespionage operations, many affiliated with governments. Each group has distinct ways of attacking their targets, down to the malicious software signatures they use. Several cybersecurity firms have verified Crowdstrike's findings that the perpetrators of the DNC attack were the two known Russian groups, and there is no evidence independent hackers could be separately responsible for the leaks.
While the government and FBI haven't officially pointed the finger at Russia, US officials briefed on the probe say the evidence so far points to groups known for conducting cyberintrusions for Moscow.
Experts say the DNC emails bear evidence of passing through Russian hands and look to be efforts by the Russians to first, cover their tracks and cast doubt on their role in the hack, and second, influence the US election towards Donald Trump, who has spoken favorable of Russian President Vladimir Putin and advocated weakening NATO.
The FBI put out a statement saying it was investigating.
"A compromise of this nature is something we take very seriously, and the FBI will continue to investigate and hold accountable those who pose a threat in cyberspace," the FBI said.
Why did Debbie Wasserman Schultz resign?
Update: Outgoing Democratic National Committee Chairwoman Debbie Wasserman Schultz will not open her party's convention in Philadelphia on Monday night, Wasserman Schultz told the Sun Sentinel newspaper. "I have decided that in the interest of making sure that we can start the Democratic convention on a high note that I am not going to gavel in the convention," Wasserman Schultz told the paper in an interview.
DNC Chairwoman Debbie Wasserman Schultz resigned on Sunday, in the wake of the scandal, but her departure was a long time coming.
Wasserman Schultz has served atop the DNC since 2011, keeping the Florida seat in Congress she's held since 2005 as well. She faced criticism through her tenure for both her work was the spokeswoman for the party and her ability to fundraise.
She faced more blowback during the 2016 primary cycle, especially from supporters of Sanders who saw decisions like her insistence on a small number of debates at low viewership times as an effort to stack the deck in favor of Hillary Clinton.
Wasserman Schultz was already expected to have a reduced speaking role at the DNC in the wake of the criticism and distrust from supporters of the Vermont senator, and the email leaks forced her hand to announce her resignation.
The Florida congresswoman was booed and jeered during an appearance before the Florida delegation Monday morning.
Who is in charge now?
As Wasserman Schultz becomes the outgoing chair, DNC Vice Chairwoman Donna Brazile is serving as the interim chair through the election. CNN and Brazile mutually agreed to suspend her contract as a political commentator for the network after the announcement was made on Sunday.
Other names for replacing Wasserman Schultz are also being floated.
According to a Democratic operative, Housing Secretary Julian Castro was being discussed by Hispanic leaders close to Clinton and her inner circle.
In terms of convention operations, the DNC Rules Committee tapped Ohio Rep. Marcia Fudge to fill in as permanent chair of the convention to gavel in and out each session, according to a DNC source.
What was in the emails?
Emails were apparently leaked from seven DNC officials' accounts, though CNN was not able to independently verify their authenticity. Nearly 20,000 total emails were dumped, including some that exposed distaste for Sanders within the DNC.
One email in May targeted Sanders' religious beliefs, with DNC chief financial officer Brad Marshall asking colleagues to "get someone to ask his belief" in God, without mentioning Sanders by name. The suggestion was that Sanders' faith could be a difference maker in Kentucky and West Virginia.
"This could make several points difference with my peeps. My Southern Baptist peeps would draw a big difference between a Jew and an atheist," Marshall wrote.
In another May email, Wasserman Schultz called Sanders campaign manager Jeff Weaver a "damn liar" for statements he made criticizing the Nevada Democratic Party after protests by Sanders supporters of what they said was subversion of party rules by Clinton backers.
