The Rust Belt bus tours and campaign cattle calls are far more about lingering post-traumatic stress from the Democrats’ 2016 loss than any current electoral strategy. While the traditionally blue states are likely to be crucial to Democrats in a general election, none of the three are scheduled to hold their primary vote before Super Tuesday, the dozen-state primary that’s widely expected to winnow the field in early March.

Acknowledge the shortcomings of 2016, to an extent

Of course, the 2020 race bears little resemblance to the last race — or any other primary in modern electoral history. The crowded Democratic field is four times as big as it was at its largest point in 2016, historically diverse and features the widest age gap ever seen in a primary contest. Democrats may have new opportunities in states where demographics are shifting like Georgia, Arizona and Texas. And the nominee will face a sitting president, who has shown some eagerness to intervene in the opposing party primary contest.

[President Trump’s re-election strategy involves stoking cultural and racial resentments, just as he did in 2016.]

The field of 2020 candidates is eager to reassure voters that if they win, they won’t take anything for granted, even as they handle the previous Democratic nominee with extreme care. Earlier this year, Ms. Klobuchar quickly called Mrs. Clinton to apologize, after she launched her bid with promises to win in Wisconsin that were seen as a jab at the former Secretary of State.

Still, the implicit critique rings clear to Democratic voters and donors.

“I was one of Hillary Clinton’s finance chairs and unfortunately she didn’t come into Michigan enough. They’re not ignoring us now,” said Barry Goodman, a Democratic donor in the Detroit suburbs who is raising money for Mr. Biden.

In town hall meetings and diner meet-and-greets, Democrats frequently bring up the 2016 defeat, often as an origin story for how they became more engaged in national politics.