Heading into Wednesday’s debate, Biden advisers and allies hope he can use the breathing room to portray himself as the battle-tested Democrat whom President Donald Trump is most afraid to face — and as the only candidate who has built a diverse, nationwide coalition of supporters.

“He’s been the center of attention, the center of a firing squad,” said Sen. Chris Coons (D-Del.), a top Biden campaign surrogate elected in 2010 to his old Senate seat. “I think the dynamic of the campaign has changed. There are more vigorous questions being posed about the policy positions of other candidates or about [their] background and record.

“No schadenfreude will be had,” Coons added, now that candidates other than Biden are drawing heat.

A Biden adviser pointed out that the former vice president has stemmed his slide in national polls. At the same time a pro-Biden super PAC is set to drop ads in Iowa and other early states. Biden received another boost during Tuesday’s impeachment hearings when a Republican-called witness, Ambassador Kurt Volker, dismissed Trump’s claims of corruption against Biden as “conspiracy theory.”

“We’ve had all the dirt and all the oppo thrown at us and we’re still standing,” said the adviser, explaining the campaign’s mindset on the eve of the debate.

Unlike in the previous four debates, Biden is no longer the clear frontrunner, though he leads in most national surveys as well as polls in the early states of Nevada and South Carolina.

In his stead, Buttigieg, after surging to first place in Iowa, has become the target.

“For Mayor Buttigieg, he’s going to be on the hot seat for the first time because he’s the ‘frontrunner’ In Iowa,” said Karen Finney, a veteran Democratic operative who worked for Barack Obama and Hillary Clinton’s presidential campaigns.

“This is the time where voters see how candidates can handle criticisms and attacks,” she said. “The race is very volatile and very fluid.”

In a sign of how unpredictable the primary is, candidates are still exiting and entering the race at this late stage, with Patrick announcing his bid last week and Bloomberg expected to any day.

Some Democrats are already expressing doubts about the newcomers' viability.

“The Democratic electorate, the voters who need to pull the levers first, are eager for a narrowing of choices. I don’t think they view either [Patrick or Bloomberg] as supplying a trait or a record that doesn’t somehow already exist in the current field,” said Ken Snyder, a Democratic strategist who worked on John Hickenlooper’s presidential campaign before he dropped out. Speaking of Biden, Warren, Bernie Sanders and Buttigieg, he added, “They’ve been thoroughly vetted and they remain frontrunners for a reason.”

As a debate rages over whether the entry of Patrick and Bloomberg would erode Biden’s lead, advisers and supporters see an opportunity to portray him as the tried and true Democrat who has shown he can take a punch.

Patrick is already facing negative press — from his time working for Bain Capital and subprime mortgage lender Ameriquest, to his past refusal to release his income taxes. (The Patrick campaign told POLITICO on Tuesday that he will release his tax returns during his campaign.)

Bloomberg is doing cleanup on his years as mayor, including on Sunday when he apologized for the “stop-and-frisk” policing strategy in New York that disproportionately targeted minorities.

“Another guy from New England, another New York billionaire. I don’t know who they think is going to jump off of whatever candidate they’re on right now,” said former South Carolina Democratic Party Chair and Biden supporter Dick Harpootlian. “I don’t see the constituency for them.”

Harpootlian also pointed out that Buttigieg had almost no black support in a batch of newly-released polls of South Carolina. In contrast, Biden is at 44 percent with African-Americans in polls of the state.

One Biden supporter pointed out that if the 77-year-old Bloomberg joins the race, it would make Biden the third-oldest candidate in the field. (Biden turns 77 on Wednesday, and Sanders is 78.)

“Did we need another septuagenarian in the race?” asked Paul Maslin, a Democratic pollster who worked for Jimmy Carter and Howard Dean’s presidential campaigns.

Maslin pointed out that Bloomberg’s likely entry in the race will help Buttigieg “play the generational card” by pointing out he’s nearly half the age of the candidates who are older than 70: Bloomberg, Biden, Warren and Sanders.

However, he said, Buttigieg could help Biden by costing her a win in Iowa while jumbling the race in New Hampshire. If the polls hold, Biden could then win in Nevada and South Carolina, heading into Super Tuesday with more wins than any other candidate.

“Buttigieg is sort of a blocking back for Biden in that scenario,” Maslin said.

Terry Shumaker, a longtime Biden friend and former U.S. ambassador who co-chaired Bill Clinton's New Hampshire campaigns, argued that after all the ebbing and flowing in the field, the primary will end up turning on one central question.

“It comes down to, ‘Who do I think can beat Donald Trump?’ I think they’re going to come home to Biden,” Shumaker said. “If he holds up to all this, which I believe he will, those questions about his age or stamina will dwindle. This election is so serious to most people, they want to get it right.”