In their view, Patrick and Bloomberg are stalking horses for moderate Democrats, high-dollar contributors and bundlers desperate to halt the momentum of the economic populists at the top of the polls — and regain control of the party levers.

It’s no minor intra-party spat in an election where all wings of the Democratic Party will need to be working in concert to beat Trump.

“There’s clearly anxiety from parts of the Democratic Party establishment and donor class about becoming a party that is unapologetic about taking on oligarchs, whether they’re Donald Trump or Jeff Bezos,” said Waleed Shahid, a former Sanders aide who now works for the progressive group Justice Democrats. “While he’ll basically try to buy votes through tons of ads, billionaire candidates like Bloomberg remain deeply unpopular. Deval’s supporters compare him to Obama, but forget that Obama also ran as an outsider populist in the 2008 primaries.”

Progressives’ concerns have heightened amid recent advances by their standard-bearers. Warren has risen to the top of the field in Iowa and New Hampshire. Sanders has enjoyed a comeback in the past month as well, receiving key endorsements and a small bump in early-state surveys after suffering a heart attack. Sanders and Warren reported having about $34 million and $26 million on hand, respectively, in their latest campaign finance filings.

“I see Deval Patrick as nothing but a kamikaze candidate,” said Murshed Zaheed, a Megaphone Strategies partner and former Harry Reid aide who supports Warren. “These folks have entered specifically in reaction to Warren’s ascendant candidacy.”

Former Massachusetts Gov. Deval Patrick. | Charles Krupa/AP Photo

Party donors and moderates dismiss those characterizations, arguing that they are simply keeping the long game in mind — winning, followed by governance. They say that even if they personally like some of the left-wing policies, Warren and Sanders will become irreparably tarnished in a general election.

“The middle is trying to be responsible and actually operate,” said one West Coast-based bundler who is hopeful that Bloomberg will throw his hat in the ring. “At the end of the day, you can say whatever you want. If it doesn’t have any chance of getting passed, what good is it?”

The person added that while Joe Biden initially looked like the most electable contender, he has proven himself to be “weak as a candidate — but more importantly, he’s weak financially.”

The Bloomberg trial balloon and last-minute Patrick campaign have come after Biden, once the hope of many moderate Democrats, has slumped in early-state polls and disclosed that he only has $9 million cash on hand.

Ari Rabin-Havt, Sanders’ deputy campaign manager, told POLITICO: “I think the high-dollar donor class of the Democratic Party is extremely nervous about having a president of the United States who is not in their pocket.”

An adviser to Bloomberg said the former New York City mayor will support whoever the Democratic nominee is. But the fact that Trump and the Republican National Committee raised $125 million in the latest fundraising quarter and a recent New York Times/Siena College poll showed Warren losing to or tied with the president among registered voters in five of six battleground states, the person said, should be concerning to anyone who wants to defeat Trump.

The same survey found Biden leading Trump among those voters in four of those states; Sanders was ahead of Trump in Pennsylvania, Wisconsin and Michigan, which were key to Trump’s victory, but behind him in three others.

“The only candidate Mike is trying to stop is Donald Trump,” said Jason Schechter, a spokesman for Bloomberg.

Patrick was greeted by a smattering of polite applause in his debut appearance Saturday at the California Democratic Party’s convention here, but also faced a heavy dose of skepticism from left-leaning delegates.

Asked about charges from progressive Democrats that he and Bloomberg represent a last gasp from the donor class and moderate Democrats to put down the progressive movement, Patrick cited his work as a civil rights lawyer and in government and industry, telling reporters, “Have a look at what I’ve been doing for most of my professional life.”

He said his record as Massachusetts governor was not “a non-progressive record,” and he said, “I’ve continued to be a progressive in the business sense by pursuing [social] impact investing.”

“Now, having said all that, don’t put me in a box,” Patrick added. “I don’t fit in one. By the way, neither do most voters.”

Both Warren and Sanders have not only proposed wealth taxes on the uber-rich, but also taken outright joy in railing against billionaires. Warren is currently selling “Billionaire Tears” campaign mugs on her website, while Sanders recently said, “I don’t think that billionaires should exist.”

In addition to being a billionaire himself — his estimated net worth is upwards of $53 billion — Bloomberg has a history with Warren. He endorsed her Republican opponent, Scott Brown, during her 2012 Senate campaign.

Months ago, Amazon CEO Jeff Bezos asked Bloomberg to think about running for president, but he declined at the time. Patrick worked at Bain Capital, the private equity firm that served as a boogeyman of liberal Democrats and former President Barack Obama’s re-election campaign, until last week.

To many on the left, that’s prima facie evidence that Bloomberg and Patrick are agents of a moneyed, ruling class determined to protect its interests against a rising progressive populist revolt.

“I think the reality is that we’ve got two super-rich guys who are scared to death that a progressive’s going to win the primary and then win the general,” said Charles Chamberlain, chairman of the progressive group Democracy for America. “This is about fear of victory, not fear of loss.”

David Sirota, Sanders’ speechwriter, wrote in an email to supporters last week that “the potential last-minute candidacies of corporate titans are a direct response to the Bernie Surge.”

While on the campaign trail in New Hampshire last week, Warren was asked about Bloomberg and Patrick. “I’ve noticed that billionaires go on TV and cry. Other billionaires encourage their billionaire buddies to jump into the race,” she said. "I believe that what our election should be about is grassroots."

Sen. Elizabeth Warren. | Sarah Rice/Getty Images

The suspicions about Bloomberg and Patrick demonstrate the deep fissures between the moderate and liberal factions of the Democratic Party. Many Democratic officials believe they lost the 2016 presidential election, in part, because of those divisions.

Jamal Raad, a veteran Democratic strategist and adviser to Washington Gov. Jay Inslee, who dropped out of the presidential race this summer, said Patrick’s candidacy is not born of altruistic concerns about electability, but “the concerns of the donor and financial class.”

Noting polls that suggest the Democratic electorate, at large, is satisfied with its presidential choices, Raad said, “The vast majority of Democrats are super happy with their choices right now.”

Progressives bombarded with concerns about electability point to the 2016 election as evidence that centrists can lose, too. “Wishy-washy corporatism doesn’t sell,” said Jeff Cohen, co-founder of the pro-Sanders online activist group RootsAction.org .

Left-wing activists have embraced any sign that a Bloomberg or Patrick candidacy could backfire. Last week, Sanders fans excitedly shared on social media a Reuters-Ipsos poll that showed Sanders and Biden were tied nationally — if Bloomberg joined the race. Without him, Biden led the field by five points.

“These other candidates, whether they’ve come from Bain Capital or they’ve amassed their own private fortune that they’re going to use to try to buy the election, that’s not really competition for Bernie Sanders,” said Jeff Weaver, Sanders’ senior adviser.