PHILADELPHIA — In the wake of Hillary Clinton's expansive victory in the New York primary, both she and challenger Bernie Sanders face a freighted decision: whether, and how, to pull back on rhetoric that has grown sharper and nastier in recent weeks as they battle for the Democratic nomination.

Both candidates are seeking delegates in Pennsylvania and in four other states Tuesday. But neither wants to risk alienating voters by coming off as too negative. Both candidates — particularly Clinton, the leader in delegates — are looking at the difficulties inherent in unifying a fractured party in November.

Part of the dilemma is that each blames the other for escalating the negativity in recent weeks — and thus each is waiting for the other to change the tone.

Sanders' chief strategist, Tad Devine, put responsibility for changing the race's tone on Clinton's campaign.

“Bernie always wanted to have just an up-or-down debate on the issues,” he said. “If they want that, they can have it. If they're going to run the kind of campaign they ran in New York, there's going to be a tough response from Bernie. He's not just going to take it.”

Sanders sequestered himself in Vermont on Wednesday to “recharge.” When he arrived home Tuesday night he spoke optimistically about winning the next batch of states, where Clinton is generally ahead.

The Sanders campaign expected better results in New York, where Clinton won by 16 points. That gave her a net gain of 33 delegates, nearly wiping out the 45 delegates Sanders won in his last five victories.

Sanders' campaign manager, Jeff Weaver, said Tuesday night on MSNBC that Sanders would spend the period before the July convention attempting to flip superdelegates, party leaders who have pledged their support to Clinton.

“At this point, yes, absolutely,” Weaver said, implicitly acknowledging that Sanders will not have enough pledged delegates.

But Devine said that finishing with more pledged delegates remains the goal. He said the campaign was looking forward to “a brilliant winning streak through California and New Jersey” which both vote on June 7.

Whether Sanders adjusts his approach will become apparent when he arrives in Pennsylvania on Thursday.

The tone of the New York campaign, if anything, heightened concerns about the willingness of all Democrats to rally around the eventual nominee.

Sanders outraged Clinton's side by declaring her unqualified for the presidency because of her vote for the Iraq war, her campaign fundraising and her links to Wall Street firms. Clinton outraged Sanders by hitting him hard on the gun immunity vote.

Robert Reich, a UC Berkeley professor who is a prominent Sanders backer and served as Bill Clinton's secretary of Labor, suggested Wednesday that both teams pull back.

“I want to urge Bernie supporters to tone down negative characterizations of Hillary and Hillary supporters to do the same with regard to Bernie,” he wrote in a Facebook post. “I know both candidates personally. Both are thoughtful and dedicated people who care deeply about this nation. Either of them would be a thousand times better president than any of the Republican candidates.

“But we will need to join together to ensure that one of them becomes president. It's important that we not jeopardize that future joint effort through excessive divisiveness now.”

Tribune Newspapers' Mark Z. Barabak in New York and Noah Bierman in Philadelphia contributed.

cathleen.decker@tribpub.com