The gloves are officially off.

Sen. Bernie Sanders' campaign hit back Tuesday at anti-Sanders Democrats in a fundraising email that followed a New York Times story on how they were agonizing over the possibility of him winning the party's presidential nomination.

That followed an earlier battle between Sanders, I-Vt., and the Center for American Progress, a liberal think tank with strong ties to the Clintons, in which the Vermont senator accused CAP of smearing progressive candidates. That back-and-forth is a microcosm of the long-running feud between Clinton allies and the Sanders operation that stretches back to the 2016 cycle.

The fundraising email included an image of the Times' headline, which read, "'Stop Sanders' Democrats Are Agonizing Over His Momentum." Sanders' campaign manager Faiz Shakir wrote: "The Democratic establishment and high-dollar donors are already planning how to stop our campaign. They are terrified of our movement — as they should be."

"But we cannot underestimate what they will do to try to take us down," the email continued.

"This isn't just an attack on Bernie. It's an attack on all of us — on everything our movement stands for," it added.

In a separate email to supporters, Shakir addressed the Times' story, saying, "Here comes the kitchen sink."

"This is a serious threat to our campaign, and we need to treat it as such," he wrote.

The Times reported Tuesday that mainstream Democrats are becoming worried that Sanders could complicate their effort to defeat President Donald Trump. Some Democrats are starting to ask how they could thwart the democratic socialist's campaign without reinforcing Sanders' sentiment that the establishment is against him, the article said.

"There’s a growing realization that Sanders could end up winning this thing, or certainly that he stays in so long that he damages the actual winner,” David Brock, the liberal operative and founder of Media Matters, told The Times, adding that he's had conversations with others about an anti-Sanders campaign that should start "sooner rather than later."

So far, Sanders has outraised his 2020 Democratic counterparts and finds himself in first or second place in early primary polling. With pressure mounting for him to do so, Sanders released 10 years of his tax returns Monday.