After months of growing calls for him to run, the vice president’s tide began turning this week after the first Democratic debate, which softened concerns about front-runner Hillary Rodham Clinton while obscuring any obvious rationale for Biden to run. But in a letter to former Biden staffers late Thursday, one of Biden’s closest advisers traced the contours of the argument Biden would make, and suggested a decision to run could be imminent.

“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,” former Sen. Ted Kaufman said in an email to a list of “Biden alumn.” The letter was obtained by The Associated Press.

Kaufman, who served as Biden’s chief of staff for two decades before replacing him in the Senate, has been at the vice president’s side for months, brought back into the immediate fold after Biden’s son died in May. He and two other aides have formed a protective and tight-lipped ring around Biden as he ponders a 2016 campaign.

“If he decides to run, we will need each and every one of you — yesterday,” Kaufman said, alluding to the breakneck speed at which Biden would have to ramp up a campaign after waiting this long to enter. Kaufman said he was confident Biden understood “the practical demands of making a final decision soon.”

Although Biden’s small team has been drafting a campaign blueprint and screening likely staffers for months, the letter to Biden’s former Senate, White House and campaign aides marked the most direct call to date for support for a potential campaign. It came as a growing number of Democratic leaders, including Clinton’s campaign chairman, expressed frustration with Biden’s delays and questioned whether it was already too late.

Yet even in the face of such skepticism, Biden has remained actively engaged in feeling out a potential campaign, placing calls this week to key Democrats in early primary states like Iowa and New Hampshire, said several individuals familiar with the conversations. These individuals weren’t authorized to comment publicly and requested anonymity. Still, they insisted that Biden had not yet made a final call.

In the letter, Kaufman didn’t identify specific policies Biden would propose if he ran. But in describing the approach the vice president would take, the letter drew an implicit contrast with Clinton, who has been criticized by some as a candidate for appearing calculated or overly choreographed.

“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.”

“He believes we must win this election,” Kaufman added, previewing a likely argument that Biden represents the best chance Democrats have to protect President Barack Obama’s legacy. “Everything he and the president have worked for — and care about — is at stake,” Kaufman said.

Biden hasn’t spoken publicly about his deliberations in weeks, dodging shouted questions from reporters during public events this week. Kaufman said Biden’s top consideration was “the welfare and support of his family,” a reference to doubts Biden expressed in September about whether he and his family were emotionally ready to run while still grieving the death of former Delaware Attorney General Beau Biden.

It was unclear whether Biden’s renewed signal of interest would be enough to keep his name in serious contention — or for how long. The first filing deadlines for primary states are about two weeks away, and Clinton and Sen. Bernie Sanders both raised more than $25 million in their last three-month stretch, illustrating Biden’s immense disadvantage.

“The indecision becomes a problem for people,” said Sam Tenenbaum, a Biden supporter and longtime Democratic donor in South Carolina. “They’re sympathetic, but I think you’ve got to make up your mind.”