MANCHESTER, N.H. — Democratic leaders have edged toward the brink of open war with one another in recent days after a series of jarring setbacks that could jeopardize the party's chances against President Trump, who continues to solidify his iron-fisted control over the Republican election apparatus.

The infighting focuses largely on the failed caucus process in Iowa, with state and national Democratic leaders at odds over who deserves blame, as well as an increasingly bitter dispute over the rules governing who gets into future nationally televised candidate debates — a process that could allow billionaire Mike Bloomberg to make the stage later this month.

In a particularly stark sign, supporters of Sen. Bernie Sanders (I-Vt.) have returned to bashing the Democratic National Committee, reviving grievances from the divisive 2016 primary race. In that campaign, Sanders backers said that the system had been stacked against the democratic socialist — a view later affirmed when WikiLeaks released hacked internal emails — and supporters of nominee Hillary Clinton blamed Sanders for failing to sufficiently rally his base on Clinton’s behalf in the general election.

A chaotic Iowa caucus has left the Democratic Party scrambling for clarity in New Hampshire. (The Washington Post)

Sanders’s allies are again charging that the DNC is maneuvering to thwart his anti-establishment movement. They say the DNC’s decision last week to call for a “recanvass” in Iowa threatened to undercut Sanders’s ability to claim momentum from winning the popular vote there, while changing the rules to benefit Bloomberg reflects the desire among the party elite for a savior to deny Sanders the nomination.

“They can shout unity all they want, but the actions show otherwise,” said Nina Turner, a national co-chairman of the Sanders campaign.

The brew of resentment and anxiety represents a sharp turn for a presidential primary race that began last year with a historically diverse field and intense optimism that Democrats could harness the same energy that helped them win big in 2018.

Now party unity is breaking down just as voters express rising concerns that none of the remaining candidates is fully equipped to take on an incumbent president who regularly scoffs at political norms of civility and accuracy.

Like Iowans, many of whom remained undecided until the last moment before the caucuses, about a third of New Hampshire voters remain undecided, with Sanders and former South Bend, Ind., mayor Pete Buttigieg appearing to have momentum before the Tuesday primary. The longtime national polling leader, Joe Biden, who many Democrats hoped would unify the party and pose the greatest threat to Trump, posted a disappointing finish in Iowa and has been sliding in New Hampshire.

The party’s internal strife now looms over the Tuesday vote here as well as additional primaries set for the coming weeks.

Advisers to the two men most responsible for overseeing the disastrous Iowa caucuses, national chairman Tom Perez and Iowa chairman Troy Price, have been privately deflecting blame onto each other, as the relationship between the two has become tense, advisers say. Price has refused to join Perez in calling for a recanvass of voting records in the state, after finding out about Perez’s demand from a deputy a few minutes before it was tweeted, people familiar with their communication said.

Price allies blame Perez for the botched caucus count, pointing to new party rules he implemented around transparency and accessibility that increased the burdens on the state. They also point to confusion over whether a cybersecurity team sent by Perez fully reviewed the technology that failed on caucus night.

“Ultimately this is the national chairman’s mess. He is the one who asked us to do it. We tried to do it. We got bushwhacked by a bad system, and now we are trying to clean up,” said former congressman Dave Nagle, who planned the 2020 caucuses with Price and now refers to Perez with the nickname “Pontius Pilate.”

In response, aides to Perez, who was not in Iowa for the caucuses, have maintained that the state party was ultimately responsible for administering the caucuses, choosing a technology vendor and making sure the technology worked. The DNC hired experts, they say, to review the cybersecurity of the technology but not the functionality of the software.

“I am not Troy Price’s boss so it is not our role to micromanage every element of the administration of elections,” Perez said in an interview Sunday, when asked about the DNC’s responsibility for the Iowa failures. “Every state party has its own process.”

Perez did not appear in the spin room after Friday’s New Hampshire debate, and he skipped a speaking slot Saturday in Manchester at a state party fundraiser because of a conflicting, and previously scheduled, appointment to meet with governors in Washington, his aides say.

From the moment he took the job as party chairman, Perez has said he is more focused on beating Trump than expanding “my holiday card list.” The party he inherited was a skeletal operation, gutted and demoralized after Clinton’s 2016 loss and the scandal sparked by leaked internal party emails, which the intelligence community has blamed on the Russian government.

Perez moved quickly to remake the nominating process, forcing more regulation of states that host caucuses, investing heavily in technology security efforts and eliminating any chance of a decisive vote by party insiders on the first ballot at the nominating convention, a concession to Sanders supporters who wanted the process to more directly reflect the popular vote.

At the start of the campaign, Sanders advisers repeatedly praised Perez, encouraging party leaders who are wary of the enormous funding advantages of the Republican National Committee, which has raised $194 million in the current election cycle compared with $76 million by the DNC, according to the Center for Responsive Politics.

But that tone shifted in recent weeks, as Sanders surrogates, supporters and staff have criticized Perez for changing the debate rules and for the appointees he has placed on the various convention committees.

Perez announced last month that he would allow candidates to make the debate stage in late February if they met either a polling threshold or won national party delegates in Iowa or New Hampshire. Perez dropped a requirement that forced candidates to attract thousands of grass-roots donors, which Bloomberg would not meet since he does not accept donations.

A former New York mayor, Bloomberg gave more than $1.5 million to the national and state parties in the final months of last year, according to federal election records. He so far has collected only one of the four 10 percent polls he needs to qualify for the Las Vegas debate Feb. 19.

Perez said the rule change was not made to benefit any single candidate.

“Our job at every debate is to identify through the most relevant measures who are the most viable candidates who should be on the debate stage,” he said when asked why he dropped the donor requirement. “The polling is now more probative because people are paying attention.”

Sanders has been blunt in his condemnation of the move.

“I think it is an outrage,” he told reporters Thursday. “I guess if you’re worth $55 billion, you can get the rules changed.”

One top Sanders aide warned that the rule change could hurt party enthusiasm.

“The question is, are working people going to turn against the Democratic Party because there is a billionaire who is himself able to get on the debate stage because he got special treatment?” Sanders senior adviser Jeff Weaver said.

Biden also has joined in the criticism of Perez for changing the debate qualification rules in a way that could allow Bloomberg onto the stage.

“The rules seem to be changing a little bit,” he said at a Saturday campaign stop, noting that other candidates had tried to change them. “If I’m Julián Castro or I’m a couple other guys — they didn’t change the rules to allow me to stay on the debate stage. But now the rules get change to put someone else on the debate stage?”

Other Democratic insiders have tried to paint the Sanders complaints as politically expedient. Along with other candidates, they say, the Sanders campaign supported a change to the debate rules in December that would have allowed candidates to qualify with either polling or donors, as part of an effort to allow Sen. Cory Booker (D-N.J.) to join the Jan. 14 debate. That change, which Perez did not accept, would also have cleared the path for Bloomberg.

The Sanders campaign was also alarmed when Perez decided last month to name his allotted appointments to the standing committees for the party’s national nominating convention, set for this summer in Milwaukee. Previous party chairmen have made similar appointments, which make up a minority of the full committee membership.

“The deck is stacked against fairness,” Turner said of the committee appointments. “And not only stacked against Senator Sanders, but it’s stacked against any candidate who is not entrenched in the elite section of the Democratic Party. And the sad thing about it is Chairman Perez knows this.”

Weaver has tried to strike a less aggressive tone, saying that the Sanders campaign still believes Perez has tried to be evenhanded. “Of course, given our experience, we are ever vigilant,” he said.

Several national committee members were upset earlier this year when word spread that the budget committee had approved transition payments equal to four months’ salary for Perez and his top deputies. The funds were intended to assure that Perez and his deputies had time to work with their successor in 2021, or this year if the party nominee calls for new leadership before the election.

“This is not a Tom thing. This is a business thing,” said Dan Halpern, budget committee chairman. “This is an effort to make sure that the DNC is a going concern.”

Perez and his team quickly distanced themselves from the effort.

“One hundred percent of our resources are going toward beating Donald Trump,” said Xochitl Hinojosa, DNC communications director. “DNC leadership will not accept any extra compensation recommended by the budget committee, which didn’t operate at the direction of DNC leadership.”

The next logistical test for Perez will come Feb. 22, when Nevada Democrats hold the second major caucus of the process. The state party has scrapped plans to use a similar app to the one that performed so poorly in Iowa, but a computer system is still expected to be employed to collate early voting results. As in Iowa, the Nevada state party has primary responsibility over the process, Perez said.

“Our goal is we want to make sure that we have a caucus that is as low tech as humanly possible while still being efficient,” Perez said. “We are working with them and we are coordinating with them.”

Sanders, meanwhile, has put a bit more of an anti-establishment edge on his speeches this weekend, perhaps aimed at the independent voters who can participate in the New Hampshire primary, many of whom are skeptical of Democratic Party leadership and other institutions.

“We’re taking on not just the whole Republican political establishment,” Sanders said, “we’re taking on the Democratic establishment.” When Sanders said the Democratic establishment was getting nervous, the applause was louder.

Voters have increasingly brought up complaints about the national party on the campaign trail, especially at Sanders events. After the Iowa caucuses, Jared Saunders, 43, drove from Massachusetts to Derry, N.H., where he raised his anxieties with Sanders directly during a town hall meeting about the recent appointment of standing committee members.

Sanders encouraged supporters to channel their nervous energy into voting for him.

“What we can do right now is make sure we have the largest voter turnout in the history of New Hampshire,” he said, drawing applause from the crowd. “The truth is that the nominee will have enormous power over those committees, okay?”

The candidate’s response did not quell Saunders’s concerns.

“The DNC rigged it in 2016 and it’s doing it again,” he said after the event.

Matt Viser and David Weigel in New Hampshire and Isaac Stanley-Becker in Washington contributed to this report.