(CNN) The word "love" has been central to Cory Booker's presidential campaign — but talk to his team today, and the word "fighting" comes up a lot.

Fighting to make the debate stage. Fighting for diversity in the Democratic primary. Fighting against a tide of spending by two billionaire candidates. Fighting, most fundamentally, for survival.

Booker will likely lose one of those battles Thursday, when he is expected to fall short of the Democratic National Committee's polling threshold for the December Democratic debate -- the first time he has missed a debate stage. A few weeks ago, it wasn't clear whether the New Jersey senator's campaign could recover from such a blow.

But Booker isn't folding. On Friday he will return to New Hampshire -- back to the campaign trail, back to business as usual.

"We're still here," said Booker's campaign manager Addisu Demissie. "We're definitely fighting an uphill battle, but we're fighting."

A few weeks ago, Demissie "didn't know" whether Booker would have a realistic path to victory without a spot on the debate stage, he told CNN on Wednesday. Reflecting the importance Booker's team placed on making the debate, they had shifted their entire campaign focus to persuasion in an all-out sprint to net enough polls to earn Booker a lectern.

That was then. Now, Booker's campaign views missing the debate is a setback, not a death sentence. Or, as Booker's New Hampshire adviser Jim Demers sees it: "It's not the end of the world, and it's not the end of the campaign."

"Sure, it matters," Demissie said. "But I don't think it matters in the same sense that it mattered for us two weeks ago."

What changed between then and now, of course, was Sen. Kamala Harris' shock decision to drop out of the race president -- a development that shook Democrats awake to a winnowing field with diminishing diversity , and allowed Booker to step into the breach with a message of righteous indignation.

Democrats responded with a wave of donations to Booker, amounting to the best online fundraising period of his campaign to date. By the weekend, he had raised more than $1 million. Whereas Booker's campaign ordinarily would have depended on a debate stage for media oxygen and fundraising fuel, they suddenly had both.

On the ground, meanwhile, the campaign has been buoyed by larger than normal crowds and early state endorsements that have continued to roll in, despite Booker's dimmed prospects for the December debate. During a swing through Iowa last week, a few Democratic activists decided to spontaneously announce their support for Booker at his events.

"I think it tells you how committed people are to Cory's candidacy," said Jerry Crawford, a veteran Iowa Democratic operative who is supporting Booker. "It tells me he's still in this."

Mere survival does not win presidential primaries, as former Republican presidential hopeful John Kasich can attest. And Booker has a long climb out of the low single digits to the top tier in any of the early primary states -- a source of "frustration," according to one Booker ally.

"They're running a textbook campaign," the supporter said, "and yet the poll numbers don't seem to reflect that."

But Booker's orbit describes a campaign organization that remains relentlessly upbeat and optimistic, like the candidate himself -- in contrast to the final days of Harris' campaign, when staffers and allies anonymously dished on the organization's woes.

If Booker is staying in the fight, however, what comes next is a trickier question.

Booker has already made clear, in an interview Wednesday on "The Breakfast Club" radio show, that even if he does not make the December debate, "we still want to make the January one." Indeed, his campaign and allies believe it will be crucial, as the last major event on the primary calendar before the Iowa caucuses on February 3.

But Demissie points to two looming uncertainties that will impact their campaign and others in unpredictable ways: the upcoming impeachment trial in the Senate, which will likely hold senators captive in Washington for long stretches during January; and the January debate qualifications, which the DNC has yet to announce.

"Any decision I make or Cory makes on any given day, literally could be changed the next day," said Demissie. "Maybe that's the unique thing about the 2020 campaign, is it's about as uncertain as any presidential campaign there's ever been."

What gives Demissie hope in such a fluid, unpredictable race that has not yet gone Booker's way is his favorable ratings among early state Democratic voters, which have remained high relative to Booker's standing in the polls, or in the press.

"I mean, it's been hard," Demissie said. "But it's easy to keep fighting when you believe."

"If we can keep it going for eight more weeks," Demissie added, "we have a chance to shock the world."