"When I think back to 2016, all the things we learned about after the fact are keeping me up at night now," said Karen Finney, who was a senior Clinton advisor then. "What are the things we don't know about and can't see happening under the radar?"
Finney is also fixated on Democrats' need to listen to local operatives. Perhaps the Clinton campaign's biggest mistake in the last cycle was ignoring activists on the ground who warned that it was wrong to be complacent about Michigan and Wisconsin, both longtime Democratic strongholds.
"The campaign manager made the decision that (computer) modeling was telling him something different than the buzz on the ground," she said. "We ended up taking Black voters for granted." Clinton lost both states.
Even as the Biden campaign and allied groups are hyper-focused on mobilizing swing state Black voters, recent polling data from UCLA hasn't calmed their nerves. It showed Trump making slight inroads with Black voters younger than 45, with 21% signaling support for the president, double his share in 2016. "At this point, everything worries me," Finney said.
That sentiment is shared by the former Obama White House staffers who broadcast the "Pod Save America" program popular with liberals. The title of Monday's episode: "How Trump Can Win." They mapped out various scenarios in which Democrats could find themselves reliving their 2016 nightmare.
The hosts warned that if Trump were to quickly notch wins in Florida and Pennsylvania, Democrats would have to win every other battleground state, and election night Nov. 3 could become a gut-churning repeat of 2016's drama. They mused about the potential for underhanded tactics by a "shadow campaign" of well-funded conservative groups and fretted about disinformation driving a late surge of support for Trump.
The wave of mail voting by Democrats, while welcomed by the party, also has operatives worrying about associated risks — mail-in ballots have a higher chance of disqualification due to voter error. Democrats are also anxious that young progressives, who tend not to vote by mail, in the end won't show up to vote on election day.
"Democrats are right to be worried about turning out the youth vote," Katie Eder, executive director of the advocacy group Future Coalition, wrote in a memo to supporters. "Less than half of young people voted in the 2016 presidential election."
Yet some Democrats say the angst is over the top.
"People have exaggerated the lessons of 2016 because it was such a jolting moment," said Cornell Belcher, who was a pollster for Barack Obama's presidential campaigns. "I get the hand-wringing and the anxiousness. But for people who have done this for a living for a while, and are students of electoral politics, the fundamentals for Joe Biden are sound."