The shared offensive comes on the heels of Biden’s best fundraising quarter — he pulled in nearly $23 million — since entering the presidential race in April. And it follows recent polling that shows he remains the frontrunner in national primary polls and a top-tier contender in first-in-the-nation Iowa, which holds its caucus Feb. 3.

Many activist groups and rival campaigns had expected Biden — whose campaign once faced questions about its durability — to have crumbled by now.

At the Progressive Change Campaign Committee, co-founder Adam Green acknowledged that the former vice president’s standing has helped galvanize the stop Biden initiative. He said the group has a list of one million members to whom it’s promoting Warren and, now, criticizing Biden.

“It’s all a closing argument about electability,” Green said. “The underlying premise is that many progressive, Democratic voters are under the mistaken impression that Biden is safe or electable when he’s the least electable option we have. And that point needs to get into voters’ heads before Election Day.”

Phillipe Reines, a neutral Democrat in the primary and an adviser to 2016 Democratic nominee Hillary Clinton, said Biden’s “total turnaround” has suddenly made him a top target among the groups that vigorously oppose him.

“People are getting nervous with a month to go that his numbers are solid. And they must have been shocked by his $23 million [Biden’s fourth quarter fundraising total],” said Reines. “A cornerstone of everyone’s strategy of Biden stumbling in Iowa was being low on cash.”

The progressive, grassroots groups don’t have deep pockets — they rely on organizing muscle. While they have no plans to spend money on radio or television ads or mail against Biden, they’re leaning on their networks of dedicated activists to spread the word on the ground and on social media.

The shared message they all echoed this week: attack Biden at his perceived strong point — his potential strength over other Democrats in a hypothetical general election match-up against President Trump.

Indivisible, a liberal movement that sprung up after President Trump’s election, last month sent its nationwide membership its candidate scorecard and ranked Biden at the bottom of its list.

Green’s group on Tuesday was part of what he called “a one-two-punch: Warren served up her bankruptcy plan and didn’t mention Biden but you look in the stories and see the quotes about the political implications and why he would be ceding the economic populism mantle and the outsider mantle to Trump.”

The day before, the group demanded Biden “retract his out-of-touch remarks about women and electability” for saying at a recent Iowa event that Clinton faced sexism in 2016 but “that’s not going to happen to me.” PCCC accused Biden of implying that “electability means old, white, male, and conservative.”

Biden’s campaign declined to speak on the record for this story. An adviser said the criticisms were a “desperate attempt to distract voters” from the fact that Biden is best positioned to beat Trump.

During the same Iowa tour in which Biden mentioned the challenges Clinton faced, he also ad-libbed a new part of his immigration reform plan by saying he would require undocumented immigrants to “learn how to speak English” in order to qualify for a pathway to citizenship.

That remark prompted the Indivisible group Monday to criticize Biden for promoting an “outdated idea that all of our candidates should be beyond.”

Former Florida Sen. Bill Nelson, a Biden surrogate, pointed out that Warren, Sanders and the other Democratic senators in the race, Cory Booker and Amy Klobuchar, all voted for a bipartisan 2013 comprehensive immigration reform plan that had the English language requirement in it.

Contrary to Indivisible’s assertion, Nelson said Biden’s moderate positions make him the best general election candidate, which is why he beats Trump by bigger margins than any other Democrat in the most recent poll from Morning Consult. Progressive activists, Nelson said, don’t understand that but know that Biden is a threat to their favored candidates.

“This is their last attempt to try to derail the Energizer Bunny,” Nelson said. “Joe Biden keeps going and going straight forward and they can’t figure out why they can’t stop him. So they’re throwing the kitchen sink at him.”

That onslaught has coincided with a new round of criticisms from Sanders and Warren. Sanders unloaded Monday night on Biden during a CNN interview in which he said the former vice president won’t be able to harness the “energy and excitement” needed to turn out working and young people because of his record voting for the Iraq War and his advocacy for trimming entitlements, supporting a bankruptcy bill pushed by financial institutions and voting for trade deals.

“You think that’s going to play well in Michigan or Wisconsin or Pennsylvania?” Sanders said, referring to three of the most hotly contested swing states that Trump won in 2016.

About the same time that Sanders was teeing off on him, Biden was attending a fundraiser in New York City where activists with New York Communities for Change was protesting him for hobnobbing with billionaires. New York Communities for Change is allied with the Sunrise Movement, a group that advocates for the Green New Deal and has hounded Biden on the campaign trail.

Sofie Karasek, spokeswoman for the Sunrise Movement, said the group’s “kickoff events” at month’s end will help educate young people about “about the Green New Deal and one about Sunrise’s plan to win, and then join our ‘strike circles’ program which will give them everything they need to organize in their community in 2020. If we endorse a candidate, then the endorsement and our engagement in the primary and the general will of course be part of what we’re plugging people into.”

At the same time, Biden also appeared to have stopped a tailspin in Iowa, where he’s either tied with or marginally behind Sanders, who has a slightly bigger lead in New Hampshire, which votes Feb. 11.

Steve Schale, the head of a super PAC dedicated to helping Biden win, said the polls tell the story of why progressives are suddenly targeting Biden.

“We’re in the last 30 days of the campaign, and that’s when people who are losing start attacking,” Schale said. “It’s not surprising they’ve taken more of a negative turn when they realized that Joe Biden after basically a year of being attacked is still the frontrunner.”