For nearly a decade, Democrats have sought to frame Donald J. Trump as an aberration of the country’s democratic norms and political traditions. For Hillary Clinton in 2016, he was mounting an “an unprecedented attack” on American democracy. Four years later, Joseph R. Biden Jr. argued that Mr. Trump had eroded “the soul of the nation.”

And so it was on Tuesday night for Vice President Kamala Harris, when she stood at the site of Mr. Trump’s most infamous speech that riled up his supporters to riot at the Capitol, and tried — in a third presidential race — to unify the nation against him.

She cast Mr. Trump as a “petty tyrant.” As an impeached president seeking a return to “unchecked power.” And as a convicted felon determined to prosecute his political enemies and keep Americans “divided and afraid of each other.”

And yet, wrapped in those sharp attacks were the signs of a shifted approach. More than any of the Democratic presidential nominees who preceded her, Ms. Harris sought to balance the existential with the everyday, intertwining her argument with the economic worries that animate far more American voters.

“Here’s what I promise you: I will always listen to you, even if you don’t vote for me,” she said. “On Day 1, if elected, Donald Trump would walk into that office with an enemies list. When elected, I will walk in, with a to-do list.”

Her approach amounts to a tacit admission of an inescapable political reality. Mr. Trump is not a fringe figure. The thunderous applause at Madison Square Garden on Sunday night, not just for Mr. Trump but for some of the darker acts that preceded him, offered a vivid reminder that he has become the soul of the Republican Party. Win or lose next Tuesday, roughly half the nation has already rallied behind him.