“You can't usually close a complicated deal with 10 people in the room,” said Sen. Mark Warner (D-Va.), one of the five Democratic senators in the bipartisan group of negotiators. “So we gave Ricchetti all [the] proxy and the Republicans gave Portman their proxy … with all of us frankly playing assist roles these last few days.”

The arrangement proved fruitful — at least in the eyes of Senate negotiators and the White House. On Wednesday, senators announced a more complete framework, and the reason the negotiations made it to that juncture, many senators told POLITICO, was because of Ricchetti.

More than any other Oval Office aide, the senior White House adviser and Biden confidant is tied to the infrastructure negotiations in the Senate. Words used by lawmakers and aides to describe his approach behind closed doors border on flattery. A “critical piece of the puzzle” with “enormous credibility,” were just some of the descriptors. Both Warner and Sen. Jon Tester (D-Mont.) said Ricchetti ran point as the lead White House negotiator, shored up by countless hours of lawmaker engagement from National Economic Council Director Brian Deese and Legislative Affairs Director Louisa Terrell.

“He didn’t talk down to anybody,” said Tester. “His perspective and representing the president was critically important in getting this deal done.”

But what Tester viewed as a virtue — from the beginning, the senator said, Ricchetti wanted to get to “yes” — others viewed as a liability. Among progressives, the concern was that the former lobbyist’s “low-key” and “soft-spoken” style resulted in too many concessions simply for the sake of keeping talks moving between the parties. And for a number of Democrats in both chambers, the negotiating process Ricchetti has been a part of has often proved frustrating.

“I was not happy [with] how this was done,” Rep. Bill Pascrell (D-N.J.) said, adding that different negotiating groups kept “popping up and saying we're gonna save the world. And obviously, no one did."

At one point Portman threatened to leave funding for public transit out of the deal, according to a GOP source with knowledge of the conversations with Ricchetti. Ultimately, the deal included $39 billion for public transit — a notably smaller sum than the nearly $49 billion in the original framework agreement announced in June.

Rep. Peter DeFazio (D-Ore.), who has criticized the White House and Senate in recent weeks for ignoring the transportation bill passed in the House, said Ricchetti is aware of his concerns about the bipartisan deal, he just isn’t sure the White House counselor cares about them.

“[Ricchetti’s] listening, and we've provided paper, and we had a list of suggested and least minimal changes they could make in the bill,” said DeFazio, who chairs the House Transportation and Infrastructure Committee. “I have no idea if any of that was adopted.”

Richetti’s elevated role in the infrastructure negotiations demonstrated both the degree of trust Biden has placed in him and the degree to which the White House found it necessary to play a central role in congressional affairs. Though the small bipartisan group of senators of both parties were heavily involved in hashing out big disagreements, the president’s team — and Biden himself — were present throughout and jumped in at key moments.

For DeFazio, this was a nuisance. The congressman said that “the subject matter experts” in both the Senate and House should be writing the deal “as opposed to the three people who wrote the bill who know nothing about transportation.”

But for others, there would be no deal without him. Ricchetti’s breakthrough meeting with Portman wasn’t the first time he steered the flagging talks through rough waters. Last month, when Biden said he wouldn’t sign the cross-aisle compromise on traditional infrastructure if the Democrat-only spending package didn’t reach his desk at the same time, Republicans were furious.

To stop them from abandoning ship, Ricchetti went into fixer mode.

Republicans told Ricchetti “that if the President did not walk back what he had spontaneously said that it would bring our negotiations to a halt,” said Sen. Susan Collins (R-Maine). “And so Steve said that he would go to work on it. And he did.”

Ricchetti, who joined Biden’s vice presidential staff in 2012, is no stranger to the Hill. Over his many years as a lobbyist, his firms contracted with a long list of influential clients, including hospitals, drugmakers and telecom companies. He also spent time as a legislative aide for former President Bill Clinton. His long Washington career has led to some accusations that he’s a corporate Democrat and no friend to progressives — an accusation his defenders reject. But Ricchetti is someone more establishment lawmakers feel comfortable around and they turn to him when they need a White House ear.

During negotiations, senators said Ricchetti’s “omnipresence” over the talks helped move them along. But Ricchetti has also been careful to not get ahead of his boss, they said, taking time to run things by Biden and others at the White House before committing.

“I have known Steve a long time and have always found him to be someone you can work with,” said Portman. “He is an honest broker but also an effective advocate for his boss.”

Though Ricchetti helped shepherd the deal to this point, much work for him and the rest of the White House remains. Bill text has yet to be released and as the Senate begins debate on the deal, keeping Democrats and the 10 Republicans needed on board will be another big test. Whether amendments will be allowed could be another complicating factor. And if a bill ultimately reaches the House, it’s unclear if there are currently enough Democratic votes to pass it.

Democrats have a slim majority in the House, where Ricchetti is close to leadership. And progressives, who have tended to work more directly with chief of staff Ron Klain, have said they won’t vote for an infrastructure bill if a reconciliation package including priorities like eldercare, childcare and a clean electricity standard is not voted on simultaneously or first. Many within the House Democratic caucus have felt sidelined by the Senate process.

White House aides have long insisted that Ricchetti’s chief function in the negotiations is to secure a big infrastructure pact for the president. But in remarks to lawmakers, Ricchetti himself has made no secret of the fact that he also wants the once-in-a-century investment to be done with the help of Republicans, noting its political benefits.

After months building trust among Senate negotiators and working to make Biden’s bipartisan wish come true, the longtime Biden consigliere has a lot riding on the success of the deal.

“There were a number of times when I think Steve was putting his reputation on the line,” said Warner. “He knew for the president's agenda how high stakes this was.”

Marianne LeVine contributed to this article.