PHILADELPHIA (AP) -- Angry Democrats heckled outgoing party chief Debbie Wasserman Schultz with boos and cries of "shame!" on Monday as the party tried to recover from an embarrassing email hack that ripped open primary wounds just hours before they planned to mount a four-day showcase of unity.
Hours before she was to gavel in the Democratic National Convention, the Florida congresswoman was met by raucous activists who accused her of favoring Hillary Clinton over vanquished rival Bernie Sanders. Activists jeered and waved signs reading "Thanks for the 'help,' Debbie." Her supporters shouted them down, as Wasserman Schultz appealed for comity.
"We have to make sure that we move together in a unified way!" she said.
For Democrats who spent last week throwing stones at Republicans' troubled convention in Cleveland, the scene was a painful reminder of their own glass house. On the eve of the four-day spectacle, the 19,000 hacked emails published by WikiLeaks appeared to show top officials at the supposedly neutral Democratic National Committee working to tip the scales toward Clinton. Wasserman Schultz denied the accusation, but was forced out as chief Sunday.
The FBI issued a statement Monday saying it is investigating the hack.
"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," it said.
Clinton campaign officials pointed the finger at Russian military intelligence agencies. They accused Russia of trying to meddle in the U.S. election and favoring GOP nominee Donald Trump.
"We don't have information right now about that, but what we have is a kind of bromance going on between Vladimir Putin and Trump which is distinct from this leak," Clinton adviser John Podesta said in an MSNBC interview.
Trump dismissed the suggestion in a tweet: "The joke in town is that Russia leaked the disastrous DNC emails, which should never have been written (stupid), because Putin likes me."
It wasn't immediately clear how WikiLeaks received copies of the internal Democratic emails. Party officials learned in late April that their systems had been attacked after they discovered malicious software on their computers.
A cybersecurity firm they employed found traces of at least two sophisticated hacking groups on their network - both of which have ties to the Russian government. Those hackers took at least a year's worth of detailed chats, emails and research on Trump, according to a person knowledgeable of the breach who wasn't authorized to speak publicly about the matter.
The emails re-emphasized a rift that threatens to undermine the Democrats' attempt to display four days of focus on putting Clinton in the White House.
The party announced Monday it would kick off its convention with a lineup of speakers aimed at easing the tensions. Massachusetts Sen. Elizabeth Warren, a progressive favorite, will deliver the convention keynote. Sanders and first lady Michelle Obama will also take the stage.
But Wasserman Schulz's plans to open the convention Monday afternoon - risking more boos on live television - raised the possibility of further drama.
"I can't say what is going to definitely happen, there is just a general feeling of unease and unhappiness and distrust," said Maggie Kain, a Sanders delegate from Rhode Island.
Republicans relished Democrats' pre-convention tumult, just days after they bumped and bumbled through their own gathering. Trump declared on Twitter: "The Dems Convention is cracking up."
Resistance to Clinton was on display during a demonstration Sunday as many thronged to a main thoroughfare and chanted, "Hell no, DNC, we won't vote for Hillary." Still many delegates, and Sanders himself, said they planned to fall in line, mindful of the Republican alternative.
Ohio's Michael Skindell, a Sanders delegate, said Monday he planned to "strongly support the nominee of the party."
Clinton campaigned in Charlotte, North Carolina, on Monday, serving up a harsh critique of Trump's foreign policy and what she said was his "trash talk about America."
Speaking to a convention of the Veterans of Foreign Wars, Clinton slammed many of his positions, vowing to stand by American allies, fight dictators and listen to the advice of military officials.
"You will never hear me say I only listen to myself on national security," she said.
Ahead of her speech, she secured endorsement of retired Gen. John Allen, former deputy commander of U. S. Central Command and a former commander of the International Security Assistance Force, overseeing NATO troops in Afghanistan.
Clinton is within days of her long-held ambition to become the party's official presidential nominee. She will formally accept the nomination on Thursday. President Barack Obama will speak on Wednesday night. Other high-profile speakers include former President Bill Clinton and Vice President Joe Biden.
Overcoming the lingering resentment among Sanders supporters may become the task of the week.
Kenny Madden, a Sanders delegate from Kentucky, said he doesn't "think there can be anything Bernie can say that will bring people together. I think that's going to have to come from the other side."
Associated Press writers Chad Day and Hope Yen in Washington, Alan Suderman in Richmond, Virginia, Julie Carr Smyth in Columbus, Ohio, Lisa Lerer in Charlotte, North Carolina, and Alex Sanz, Megan Trimble, Julie Pace and Kathleen Ronayne in Philadelphia contributed to this report.