Democratic Party leaders are upping the pressure on Bernie Sanders to drop his presidential campaign, alarmed that his continued presence is undermining efforts to beat the presumptive Republican nominee, Donald Trump, and again win the White House.
"I don't think they think of the downside of this," said Senator Dianne Feinstein, a supporter of front-runner Hillary Clinton and broker of the post-primary peace between Mrs Clinton and then-Illinois Senator Barack Obama in 2008.
"It's actually harmful because she can't make that general-election pivot the way she should," Ms Feinstein said. "Trump has made that pivot."
The new concerns come after Mr Sanders's recent wins over Clinton in Indiana and West Virginia.
While those victories have provided his supporters a fresh sense of momentum heading into next week's primaries in Kentucky and Oregon, they did almost nothing to help Mr Sanders cut into Mrs Clinton's nearly insurmountable lead in the delegates who will decide their party's nomination.
Still Mr Sanders soldiers on, frequently telling the thousands of supporters who attend his rallies that he still has a narrow path to the nomination.
"Please do not moan to me about Hillary Clinton's problems," Mr Sanders said in a recent interview with MSNBC. "It is a steep hill to climb, but we're going to fight for every last vote."
I've got some bad news for Trump: If I am the Democratic nominee, I'm going to defeat him, and I will defeat him by very large margins.— Bernie Sanders (@BernieSanders) May 13, 2016
Mrs Clinton, her aides and supporters have largely resisted calling on Sanders to drop out, noting that she fought her 2008 primary bid against Mr Obama well into June.
But now that Mr Trump has locked up the Republican nomination, they fear the billionaire businessman is capitalising on Mr Sanders's decision to remain in the race by echoing his attacks and trying to appeal to the same independent, economically frustrated voters that back the Vermont senator.
"I would just hope that he would understand that we need to begin consolidating our vote sooner rather than later," said Steve Israel, a Clinton backer and former chief of efforts to elect Democrats to the House. "Democrats cannot wait too long."
Though Mrs Clinton has for the past few weeks largely focused her rhetoric on Mr Trump, campaign aides say the two-front effort hampers their ability to target both Sanders supporters and Republican-leaning independents that may be open to her candidacy. It also means she is spending time in primary states, rather than battlegrounds that will decide the general election.
Mrs Clinton will return to Kentucky on Sunday, two days before the state's primary.
She is sending high-level advocates to the state this weekend to rally voters, among them Virginia Senator Tim Kaine, former Pennsylvania governor Ed Rendell and Representatives James Clyburn of South Carolina, GK Butterfield of North Carolina, Sheila Jackson Lee of Texas, and Hakeem Jeffries and Joe Crowley of New York.
While they can talk up Mrs Clinton, Mr Sanders's determination to contest every state remaining has kept Mr Obama and Vice President Joe Biden largely on the sidelines, benching two of her most powerful advocates.
"It all sort of slows the take-off of her general-election campaign," said Ohio Senator Sherrod Brown, a member of the party's liberal wing from a perennial battleground.
Mr Sanders's campaign saw its fundraising drop by about 40% last month and he has laid off hundreds of staffers. Mr Biden said this week he "feels confident" that Mrs Clinton will be the nominee.
Even Mr Obama is pointing out the realities of the delegate maths, which puts Mrs Clinton on track to capture the nomination early next month.
Mrs Clinton has won 23 states to Mr Sanders's 19, capturing three million more votes than her rival along the way. She has 94% of the delegates needed to win the nomination, which means she could lose all the remaining states and still emerge as the nominee - as long as all her supporters among the party insiders known as superdelegates continue to back her.
Clinton campaign manager Robby Mook wrote in a memo to donors this week that there is "no doubt" Mrs Clinton will be the Democratic nominee, describing her lead as "insurmountable".
White House officials believe Mr Obama has the ability to coax some die-hard Sanders' fans into the Clinton camp, particularly young people and liberals. But if he moves before Mrs Clinton officially captures the nomination, he risks angering those voters and undermining that effort.
Mrs Clinton faces a similar calculus. While her international expertise could attract foreign policy-focused Republicans and suburban women, highlighting her record on those issues now might encourage Mr Sanders to resurrect attacks on her vote in favour of the Iraq war.
"When his rhetoric takes a sharper tone against her, the hairs on the back of my neck stand up," said Senator Claire McCaskill. "I know that can be used as ammunition."
Clinton backers say there is plenty for Mr Sanders to do in his old job - and a lot of good reasons for him to join forces. If Democrats regain the majority in the Senate, he would likely become chairman of the powerful Senate Budget Committee.
"We are looking forward to welcoming him back to the Senate," said Senator Debbie Stabenow.
Others note that Mrs Clinton has gone through this before and the party was able to unite after a tough primary in 2008.
"She knows this is a long process. It's a marathon you run to the end," said Representative Xavier Becerra. "On the Democratic side, we're attacking issues, not each other."