WASHINGTON — Joe Biden closed out his midterm campaign push with a glimpse of what might be a winning message for him in 2020, blasting President Donald Trump for “pouring fuel on a fire of intolerance” while promising that Democrats would unite the country and “finish the job Barack and I started.”

But as some other potential Democratic hopefuls quickly pivoted to begin laying the groundwork for a White House run, the former vice president, who turned 76 on Tuesday, remains in a holding pattern.

The Biden family prepares to celebrate Thanksgiving as the paperback version of his 2017 book, “Promise Me, Dad,” hits shelves. The first-person account of Biden’s closing months as vice president is centered around his eldest son Beau’s brain cancer diagnosis, and the impact Beau’s death had — and continues to have — on the Biden family.

It's the single biggest factor that kept Joe Biden out of the 2016 presidential race, and aides say it may keep him out of 2020 contention, as well.

Next month, the same weekend that New Jersey Democratic Sen. Cory Booker travels to New Hampshire, the first-in-the-nation-primary state, Biden will be in neighboring Vermont closing out a promotional tour for the paperback. It will be his main public engagement until he makes a final decision about his political future.

“It will be a family decision. And we have time,” Biden said after casting his ballot in Delaware earlier this month.

In a new afterword to the book, Biden describes a grieving process that evolved and improved in fits and starts. His first year outside the White House “had been more satisfying than I had hoped in most ways: busy, and consequential, and full of purpose.”

He also said he remains committed to keeping the promise he made to his son: "Be engaged, Dad, he was saying. Stay in the game. Keep fighting for what you believe in. Don’t give up.”

Democrats’ 2020 field could number in the dozens, and the decision from Biden, more than any other Democratic heavyweight, will determine how large it becomes. A close-knit team of aides has been working quietly to put Biden in position to wage a presidential campaign if he chooses to do so. But their preparations can only go so far without a final decision, expected by mid-January.

A top Biden aide told NBC News that Democratic operatives eager to join a Biden campaign have been reaching out to the political team. Some say they’ve received offers from other potential contenders — Booker was interviewing potential campaign managers just last week — but that they would hold out for Biden if he’s going to make the jump. No commitments are being made, the aide said.

“He has a timeline. We’re operating under that timeline,” the aide said.

Biden campaigned in the midterms with gusto, holding a dozen events in the closing week. He made calls throughout election night from to some 40 candidates he had campaigned for or endorsed — and at least one to a prominent Republican: Sen.-elect Mitt Romney of Utah.

He also placed a call to Iowa Rep.-elect Abby Finkenauer, for whom Biden had made his only trip to the first-in-the-nation presidential state. A top Iowa Democratic operative called his rally in Cedar Rapids for Finkenauer “the best, most energized political event of the midterm season.”

Biden has many other advantages with key early state activists, said the operative — who has been in touch with multiple potential campaigns and requested anonymity in discussing the field.

“He does not have to be first in and he knows that,” the operative said. “There's only really one question, and that's tell me how you win. That is the case he’ll have to make to the party faithful.”