Trump is trying to divide the left. He's actually uniting it behind Biden.

"Oh, you don't? Oh, well, that's a big statement," Trump interjected. "You just lost the radical left."

The exchange was hardly the show-stopper the President hoped for. Biden's position on the climate plan was well-known to progressive activists, who have largely been encouraged by his willingness to include some of its goals, if not its grandest ambitions, into his own proposal. But their support is rooted in more elemental concerns -- which only grow with each passing day -- over the prospect of Trump's reelection.

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"If Joe Biden wins, the left will have many opportunities to exert leverage and push him towards progressive priorities like the Green New Deal," said progressive organizer Max Berger, a veteran of Sen. Elizabeth Warren's primary campaign. "If Trump wins, we will see full blown authoritarianism in America. We're not confused about what Joe Biden or Trump stand for, or what's at stake."

After sealing the Democratic nomination in April, Biden and his team set about knitting together Democratic factions -- for at least a few months -- behind a singular, shared goal: defeating Trump in November. Those efforts, which included a series of "unity task forces" with Sanders' allies, yielded a more ambitious climate plan and gave the left's leaders some assurance that their concerns would be heard by the Biden campaign.

Still, progressive activists and high-profile lawmakers remain clear-eyed about the status of their relationship with Biden. It is one borne of convenience and necessity -- rooted in an understanding that the only path to realizing their policy agenda runs through a Democratic administration. That Biden hasn't entirely bought into the Green New Deal, and would say so publicly, surprised few. Instead, Trump's attacks have only further solidified an uneasy alliance and hardened the commitment of leading progressives, who largely view the President as an existential threat to American democracy.

To the extent there was disquiet on the left after the debate, it was over what some felt was a missed an opportunity for Biden to bolster his support with younger voters who, as Sunrise Movement political director Evan Weber told CNN, view the Green New Deal as "code for bold and progressive climate action of the scale of the crisis."

Weber also said that Sunrise made contact with the Biden campaign after the debate to offer "feedback," and described the nominee's team as "very receptive."

"The Biden campaign has worked collaboratively with Sunrise Movement, our allies like (Rep.) Alexandra Ocasio-Cortez, labor unions and frontline environmental justice communities to build a really bold and ambitious climate platform that is much stronger than what he was running on in the primary," Weber said.

Biden has not given much way on the issues that galvanize progressives -- he still opposes "Medicare for All" single-payer health insurance, is averse to liberal calls to change Senate rules in a tit-for-tat over the Republican push to confirm Trump's new Supreme Court nominee, and has kept his distance from the Green New Deal.

Trump on Tuesday night sought to exploit those divisions, prodding Biden to publicly disavow the left wing of the party and potentially depress support for its nominee.

The reality, though, was much different. Trump, perhaps more than any party leader or progressive champion, has been the glue that keeps together the seams of the Democratic coalition. His relentless and often racist attacks on members of the progressive lawmakers known as "the squad," particularly Minnesota Rep. Ilhan Omar, have the effect of closing Democratic ranks -- even for those who readily acknowledge Biden was not their first or second or even third choice going into the primary.

"I think (Trump's effort) backfired and united anti-fascist, socialists (and others) to do everything we could to elect Joe Biden, because it's not about an individual," said Alexandra Rojas, the executive director of Justice Democrats, a leading progressive group, and a CNN political commentator. "This is about, as AOC says, letting democracy live another day."

Trump, Rojas added, fundamentally misunderstood how the left views the coming election -- and had, in ignorance, projected his own way of thinking, which prizes personal loyalty over any policy-driven political agenda.

"What he doesn't understand is that we can think about not just ourselves, as individuals and our feelings and what we care about, but we can recognize there's actually this really existential threat against our democracy, our planet, our country right now," Rojas said. "And instead of looking at it and cowering in fear, we're going to tackle it head on alongside whoever's on our team right now, knowing that there's going to be lots of fights ahead when we do have, hopefully, a Democratic majority across the White House, the Senate and in the House."

The lack of interest on the left for alternatives to Biden has also been illustrated by the struggles of the Green Party, which has been polling well below its 2016 levels, and is struggling to get on the ballot in a number of states. One of the reasons, Green presidential nominee Howie Hawkins told CNN recently, was that, at least in Wisconsin, typically progressive-friendly law firms didn't return their calls or help with their access fight -- causing his campaign to turn to Republican-aligned lawyers. They ultimately lost in court.

Asked whether Trump's goading and Biden's distancing himself from the Green New Deal could threaten the relationship between the nominee and the left, Jamaal Bowman, the Justice Democrats-backed progressive who defeated New York Rep. Eliot Engel in a June Democratic primary, laughed.

"It has absolutely no effect whatsoever," Bowman said. "We are all crystal clear that we need to get Trump out of the White House -- like, yesterday. And we are all crystal clear that we need to flip the Senate and grow our numbers in the House. Because only then can we have a fully Democratic Congress and White House, and only then can we push Biden to the left in the way that we need to and hold him accountable. So when Trump does that, it has literally no effect."

The state of relations between Biden and progressives came under scrutiny following the debate, when the former vice president, on a whistle-stop tour through Ohio and Pennsylvania, told reporters he had not recently spoken to Ocasio-Cortez. He quickly followed up to note that he "appreciated her endorsement."

The Green New Deal, Biden continued, is "not a bad deal, but it's not the plan I have."

On debate night, Biden batted away Trump's frequent claim that he was beholden to the "radical left" by reminding viewers that he had defeated Sanders -- "by a whole hell of a lot" -- and said, in victory, he had become the face of the party. Biden took a softer tone the day after, but didn't back off his fundamental point.

"We negotiated, we debated and we had a primary election. And I won and I've laid out what we're going to do, so I'm not worried about losing the left, right or the center of the party," he said in Alliance, Ohio. "This is a big party. But I have one of the most progressive records (that) any Democrat's run on."

The latter claim might raise some eyebrows on the left, but with a little more than a month to Election Day, the specter of another four years with Trump in the White House has pushed intra-Democratic squabbles off the table. Sanders has led the way in framing the stakes, campaigning virtually for Biden and warning, as he did in his Democratic convention speech, of the consequences of factionalism in a political crisis.

"Under this administration, authoritarianism has taken root in our country. I and my family, and many of yours, know the insidious way authoritarianism destroys democracy, decency and humanity," Sanders said during his primetime speaking slot. "As long as I am here, I will work with progressives, with moderates, and, yes, with conservatives to preserve this nation from a threat that so many of our heroes fought and died to defeat."

His message to supporters, in smaller gatherings like a video call with delegates before the convention, has included more nuanced arguments about power and political realism. He explained that night, in an almost professorial tone, the importance of "coalition politics" and how it applied in the current context.

"In politics, you got to think long term," he said in an interview the next day. "That's what coalition politics is about. It says, look, we disagree with you on health care, we disagree with you on aspects of criminal justice. We disagree with you on aspects of education. Fine, we're going to have a fight after the election ... But right now, at this moment, we all -- and that is Biden supporters, my supporters, other candidates' supporters, independents, and Republicans -- have got to come together to defeat Donald Trump."