Former President Donald J. Trump and his allies are rolling out a late-stage campaign strategy that borrows heavily from the subversive playbook he used to challenge his loss four years ago, this time with reinforcements from outside groups built on the false notion of a stolen election.

With Election Day only three days away, Mr. Trump is already claiming the Democrats are “a bunch of cheats,” as his allies in battleground states spread distorted reports of mishaps at the polls to push a narrative of widespread fraud.

Mr. Trump and his most prominent supporters have pointed to partisan polling and betting markets to claim that he is heading for a “crushing victory,” as his top surrogate Elon Musk recently put it. The expectation helps set the stage for disbelief and outrage among his supporters should he lose.

And in a direct echo of his failed — and, prosecutors say, illegal — bid to remain in power after the 2020 election, some of his most influential advisers are suggesting he will yet again seek to claim victory before all the votes are counted, a move that ushered in his efforts to deny his defeat four years ago and helped set the stage for the attack on the Capitol on Jan. 6, 2021.

In many respects, though, the effort that led to Jan. 6 never ended.

“It’s been four years of spreading lies about elections and recruiting volunteers to challenge the system, filing litigation,’’ said Joanna Lydgate, the chief executive of States United Democracy Center, a nonprofit group that works with state officials to bolster confidence in their elections. “What we’re seeing today is all of that coming to fruition.”

The Trump campaign did not respond to an email seeking comment.

In a statement, Dana Remus, a top lawyer for Vice President Kamala Harris’s campaign, said, “It isn’t surprising that he is already questioning the results of a still ongoing election” and added, “He failed when he tried this in 2020, and he will fail again.”

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