Vice President Joe Biden would run an optimistic and unscripted "campaign from the heart" based on restoring middle-class opportunity, one of his top political advisers said Thursday, laying out for the first time the argument Biden would make if he runs for president.

Former Delaware Sen. Ted Kaufman, one of Biden's closest political advisers, said Biden would soon make a decision about whether to enter the race. In an email obtained by The Associated Press, Kaufman asked former staffers to stay in close contact and said Biden would need their help immediately if he enters the race.

"If he runs, he will run because of his burning conviction that we need to fundamentally change the balance in our economy and the political structure to restore the ability of the middle class to get ahead," Kaufman said.

Calls within the Democratic Party for Biden to run have been growing for months, fueled largely by concerns that front-runner Hillary Clinton's campaign was faltering under the weight of an email scandal and declining popularity. But Clinton's performance Tuesday in the first Democratic debate, coupled with Biden's seemingly endless delays in making a decision, have put a damper on the speculation in recent days, with top Democratic leaders questioning whether it's too late for Biden.

Kaufman's letter to former Biden aides marked an attempt by the vice president to signal he's still very much considering running and shouldn't be written off. It also served to reinforce the notion that Clinton isn't the only Democrat who could run in part on a promise to lock in policies that Obama has advanced during his two terms.

More On This...

    "He believes we must win this election," Kaufman said. "Everything he and the president have worked for -- and care about -- is at stake."

    Clinton and her top rival in the race, Sen. Bernie Sanders, have been campaigning for months and have raised tens of millions of dollars, giving them a huge head start that would make it tough for Biden to mount a viable challenge. The first filing deadlines in some states are just weeks away and Biden currently has no operation in key states. Alluding to those concerns, Kaufman said Biden was "aware of the practical demands of making a final decision soon."

    "If he decides to run, we will need each and every one of you -- yesterday!" Kaufman wrote in the letter, distributed to Democratic operatives who worked for Biden in the Senate, in the White House or on his previous presidential campaigns.

    Kaufman, a longtime Biden confidant, served as his chief of staff in the Senate and was appointed to replace him when Biden became vice president. In the weeks after the vice president's son, former Delaware Attorney General Beau Biden, died from brain cancer in May, Biden brought Kaufman back into the fold and gave him an office on the White House campus.

    He's one of three top advisers who have spent the last two months cloistered with Biden as he decides about 2016; Biden chief of staff Steve Ricchetti and political adviser Mike Donilon round out the trio. The group met with Biden to discuss the 2016 race on Wednesday evening at Biden's official residence, said a person familiar with the meeting, who wasn't authorized to speak to reporters and requested anonymity.

    Yet Kaufman and other top Biden staffers have put together a campaign-in-waiting that could be activated quickly if he decides to take the plunge, with lists of potential staffers who have agreed to work for a campaign and donors committed to helping fund it. Those discussions have all taken place in private, and Biden's office has declined to comment on the status of his deliberations.

    Kaufman's letter to former staffers opened a new, more public phase of the deliberations, as Biden seeks to keep himself in the discussion despite the fact that many Democrats have moved on or grown frustrated with his indecision. Even Clinton's campaign chairman, John Podesta, told reporters this week that it was time Biden make a decision.

    Biden's top consideration is the welfare and support of his family, Kaufman said. The vice president has said previously he's unsure he has the emotional fortitude to run following his son's death.

    "He is determined to take, and to give his family, as much time as possible to work this through," Kaufman said.

    Clinton's resurgence following Tuesday's debate has prompted questions about what rationale Biden could offer for challenging her and how he would differentiate himself from the former secretary of state he served alongside in Obama's Cabinet. But Kaufman said he'd spoken extensively with Biden about his deliberations and that if he runs, Biden would mount an "optimistic campaign."

    "A campaign from the heart. A campaign consistent with his values, our values, and the values of the American people," Kaufman said. "And I think it's fair to say, knowing him as we all do, that it won't be a scripted affair -- after all, it's Joe."