- Some Democrats worry primary season won't end on a unifying note
- Obama, Warren among the Democrats who could try to heal the party
(CNN)Democrats need a peacemaker.
The final weeks of the primary, which culminates June 7 when voters in big states including California and New Jersey head to the polls, are being dominated by rising tension between Hillary Clinton, Bernie Sanders and their supporters.
Sanders is escalating his attacks on the Democratic establishment -- even taking the unusual step over the weekend of backing the primary challenger to the chairwoman of the Democratic National Committee -- as Clinton is on track to clinch the party's nomination next month. The stakes of the fight are intensifying as several recent polls show Clinton locked in a neck-and-neck fight with presumptive Republican nominee Donald Trump in the fall.
That's leaving some Democrats worried that the primary season won't be a cathartic and ultimately unifying experience.
"I am increasingly concerned that even if Sen. Sanders would come around and support a Clinton nomination that things become so polarized that not all of the supporters would agree to do so," said Jim Manley, a former senior aide to Senate Minority Leader Harry Reid, who has publicly backed Clinton. "I am afraid he has made this internal debate so polarized that even if he comes around, far too many of his supporters would just be so disgusted with the process that they won't come out in the numbers needed."
The longer it goes on, the more the Democratic primary race seems in need of political intervention to ensure a soft landing. But just who might be best placed to successfully lead that effort is unclear, though the options include President Barack Obama and Sen. Elizabeth Warren.
For starters, Sanders is currently waging open political warfare with DNC Chairwoman Debbie Wasserman Schultz over a longstanding belief that the party establishment stacked the deck in the primary for Clinton. His endorsement over the weekend unleashed a quarter of a million dollar cash bomb for Wasserman Schultz's primary opponent, Tim Canova.
Sanders has said Wasserman Schultz would not be reappointed if he wins the presidency and their feud means she cannot play the behind-the-scenes role in unifying the party that her GOP counterpart, Republican National Committee Chairman Reince Priebus, has performed.
So if Wasserman Schultz is not available, maybe the candidates can lower the temperature themselves?
That seems a long shot, especially after Clinton went on CNN last week to declare the race "done" and as Sanders shows no sign of backing down.
He is intensifying his barrage as he goes all out for a win in the California primary on June 7 that is unlikely to snatch the nomination from Clinton but would hugely increase his leverage over the Democratic Party platform. Over the weekend, for example, Sanders suggested Clinton was the "lesser of two evils" compared to Trump in an interview on ABC's "This Week."
Their relationship took another turn on Monday when Clinton's campaign said she would not take part in a Fox News debate with Sanders before the California primary.
"I also would suggest that Secretary Clinton may want to be not quite so presumptuous about thinking that she is a certain winner," Sanders said in a sharply worded statement. "In the last several weeks, the people of Indiana, West Virginia and Oregon have suggested otherwise."
From Sanders' point of of view, after attracting millions of Democratic votes and significantly out-performing expectations, he has every right to stay in the race until the end -- and even to try to pull off a high odds attempt to overtake his rival.
All of this means that once Clinton is officially enshrined as the Democratic nominee, she will face a significant task in knitting the party together around her for a general election showdown with Trump.
Clinton spoke charitably about her opponent at a rally in Detroit on Monday, making a step towards party unity.
"I applaud Senator Sanders and his supporters for challenging us. And we are going to unify the Democratic Party and stop Donald Trump," Clinton said.
But in many ways, she appears to be the last person suitable to wooing Sanders supporters.
Only 66% of Sanders primary voters said in an NBC/Wall Street Journal poll released Sunday that they would back Clinton in a general election against Trump, compared to 88% of Clinton voters who would vote Sanders.
The former secretary of state, meanwhile, had a positive approval rating of only 38% among Sanders supporters, compared to 54% of Clinton backers who like Sanders.
Such data points to the absolute necessity for Democrats that Sanders deliver a full and unequivocal vote of support for Clinton.
For a long time, many Democrats had expected, and many polls predicted, that once their Sanders versus Clinton contest wrapped up, the party would quickly coalesce behind the winner, most likely the former secretary of state.
But some analysts are beginning to doubt that scenario.
"I am not sure that is the case," said David Gergen, a senior CNN political analyst on Monday. "We always thought that the Republicans would have fisticuffs at their convention -- she has got to come out of there united, with (Sanders) supporting her enthusiastically."
Any other outcome could be disastrous for Clinton given that a general election against Trump now looks set to be decided by the relative motivation of each side's core voters.
So if Clinton and Sanders cannot orchestrate the coming together after a divisive primary themselves -- as she and Obama did after their own fierce duel for the nomination in 2008 -- who can do it for them?
The most obvious choice is Obama himself. The President, though clearly favoring Clinton as the chosen successor who could secure his legacy, has been respectful to Sanders throughout the campaign.
The President's approval ratings among all voters have now climbed above 50%, according to several polls, and Obama remains highly popular with Democrats, meaning that he may have unique potency in the 2016 campaign.
"The most important number in a lot of these polls is the popularity of Barack Obama," said Steve Elmendorf, a deputy campaign manager for John Kerry's 2004 campaign who now supports Clinton, on CNN's "At this Hour" on Monday.
"I think Barack Obama is going to do more work than anyone to bring the party together."
The White House plans to send the President on significant campaign swings once the Democratic nominee is confirmed, senior officials have said.
And First Lady Michelle Obama is also expected to take to the campaign trail to underscore his message that protecting his legacy and keeping Trump out of the White House requires the type of Democratic coalition that came together in 2008 and 2012.
Still, Sanders has been criticized throughout the campaign -- especially by Clinton -- for not being sufficiently supportive of the President himself.
And Sanders' positions on issues like health care and Wall Street are to the left of legislation Obama has enacted -- a sign of how far the center of political gravity has shifted for Democrats since 2008.
Other Democratic luminaries may be required to help heal the party. But one party graybeard is definitely ruled out.
Given that he was the first Democrat to win two terms since World War II, in other circumstances, Bill Clinton would be the ideal messenger to his divided party.
But even if he wasn't married to Sanders' rival, the fact that some of his key 1990s policy achievements -- reforms of criminal sentencing, welfare eligibility and financial regulation -- have been repudiated by the Vermont Senator, Bill Clinton isn't likely to play a unifying role.
Other key Democrats who might nudge Sanders into cooling the rhetoric of his campaign are also hardly popular in his camp.
Reid, for example, was openly critical of Sanders over unrest that erupted at his home state of Nevada's Democratic convention this month. Chuck Schumer's name has also been mentioned as a possible go between -- as he apparently retains a warm relationship with Sanders. But the New York senator is much closer to Clinton so may not have much clout among Sanders supporters.
A CBS News report last week suggested that top Democratic senators believed Massachusetts Senator Elizabeth Warren would be an ideal emissary to Sanders' liberal supporters. But it remains unclear how well the populist Democratic heroine is connected to the top echelons of the Clinton campaign.
In the end, hopes among Democrats of a party reconciliation may depend on Sanders opting to change the tone himself, and living up to his vow to do everything he can possibly do to ensure Trump never becomes President.