Bernie Sanders made a last-ditch effort Monday to cool anger among his supporters against party leaders and Hillary Clinton, as the Democratic convention opened amid new threats to party unity.
The Vermont senator, who was booed by his own supporters earlier Monday when he spoke about the need to elect Clinton, intervened amid fury over leaked emails showing party leaders hostile to his primary campaign.
"I ask you as a personal courtesy to me to not engage in any kind of protest on the floor. It's of utmost importance you explain this to your delegations," Sanders said in a text message sent to his floor supporters in Philadelphia.
State Rep. Diane Russell of Maine, a strong supporter of Sanders, delivered a fiery speech at the convention in the afternoon intended to soothe tensions.
She argued that delegates could "stand strong with Bernie Sanders" and still "do everything you can do to elect Hillary."
Sanders is due to address the convention in a prime-time address Monday night and is expected to call for unity and to warn that lingering divisions could result in a disaster scenario for Democrats -- the election of Republican Donald Trump.
The text message appeal came about after Sanders deputy campaign manager Rich Pelletier and Clinton aide Marlon Marshall met in a bid to head off any floor protests that would shatter the image of Democratic unity as the convention opened, a party official said.
The frantic attempts to cool tempers as oppressive mid-summer temperatures stifled Philadelphia came after leaked emails published by Wikileaks, apparently the result of a Russian hacking operation, forced the resignation of DNC Chairwoman Debbie Wasserman Shultz on the eve of the convention.
Wasserman Shultz was booed by members of her own Florida delegation on Monday after the emails appears to validate long standing claims by the Sanders camp that the party had rigged the election against their candidate.
The DNC issued an apology to Sanders moments after the convention opened Monday, likely hoping to help soothe tensions heading into the week.
"On behalf of everyone at the DNC, we want to offer a deep and sincere apology to Sen. Sanders, his supporters, and the entire Democratic Party for the inexcusable remarks made over email," the statement said. "These comments do not reflect the values of the DNC or our steadfast commitment to neutrality during the nominating process. The DNC does not -- and will not -- tolerate disrespectful language exhibited toward our candidates. Individual staffers have also rightfully apologized for their comments, and the DNC is taking appropriate action to ensure it never happens again."
The DNC is facing questions about whether it could have done more to limit the damage done by hackers suspected of working for Russian intelligence. Federal investigators tried to warn the DNC about a potential intrusion in their computer network months before the party moved to try to fix the problem, US officials briefed on the probe tell CNN.
As frustration at the convention escalated Monday afternoon, the Sanders camp reached out to the Clinton campaign to express concerns over raw tensions among their delegates that could erupt into protests on the floor, according to sources. The Clinton and Sanders campaigns joined forces by syncing their floor whip teams to present a united front on the floor.
Former NAACP leader Ben Jealous will be among the Sanders surrogates deployed to the Sanders to try to urge against raucous displays.
But emotions were running high as the convention opened and chants of "Bernie! Bernie!" rang out in the Wells Fargo Center in Philadelphia --- underscoring still painful party divisions after the divisive primary.