The 2020 Democrats are playing nice. For now.

New York Sen. Kirsten Gillibrand welcomed Minnesota Sen. Amy Klobuchar's wintry announcement with a warm tweet celebrating her "Senate sisters" — a groundbreaking group of four women that includes 2020 contenders California's Kamala Harris and Massachusetts' Elizabeth Warren.

That same day, Ohio Sen. Sherrod Brown, who is considering a run, posted a 62-second video of New Jersey Sen. Cory Booker, a declared candidate, speaking to voters in Iowa. Booker, who discussed "the dignity of work," a Brown catchphrase, in the clip, retweeted his Senate colleague with an acknowledgment: "They say imitation is the sincerest form of flattery, my friend."

On Monday morning, Harris was asked during an interview with the "The Breakfast Club," a popular New York radio show, what she would do to guarantee that the eventual nominee emerges from the primary with the uniform backing of Democratic voters.

"When I first made the decision to run, I actually called a number of my colleagues who had either announced or I knew were thinking about announcing to make just that point and to reach out to them," Harris said. "I have a great deal of respect for the folks who have decided to run and I know there are others who are seriously thinking about it who I also respect."

After spending more than two years in near-unbroken opposition to President Donald Trump and congressional Republicans, the Democratic presidential hopefuls are easing into what many expect to become a rancorous nominating contest. Their public overtures to one another, a kind of ruthless friendliness, are in part a function of personal familiarity — eight or nine senators could end up running — and a fundamental understanding about the electorate: Democratic voters do not want to relive the 2016 primary.

That means the attacks, when they come, will come at a price and, because of the relatively narrow ideological gaps between some of the leading candidates, the process of picking out the profitable ones will be even more difficult.

"Everyone's trying to figure out where exactly they fit in to the process and who their competition is," said Jim Manley, who was a top aide to former Democratic Senate leader Harry Reid of Nevada. "But at some point, this going to become a battle of ideas and the rhetoric is going to get a lot tougher. For right now, if only because it's so early in the process, everybody is playing nice in the sandbox."

"They know each other, they're friends with each other's families, it's very personal and they don't need to be negative -- yet. We're early," Amanda Litman, co-founder of Run for Something and a Hillary Clinton staffer in 2016, said of the field. "It doesn't benefit them to be negative. It doesn't benefit them to be personally combative."

The new congressional class, headlined by New York Rep. Alexandria Ocasio-Cortez, has been rightly credited for pushing an already progressive slate of presidential candidates further left. But Litman also pointed to the group's frequent displays of solidarity as another way they could influence both the tone and tactics of the primary.

"There's been a really interesting dynamic modeled in Congress of all the new women supporting each other and campaigning together," she said. "I think that watching the women in Congress and seeing the positive response (and the feeling of) 'we're in this together' feeds into this idea that you gain by demonstrating allyship than you do by bringing someone else down. At least at the moment."

The increased clout of grassroots groups like Justice Democrats, the organization that recruited Ocasio-Cortez to run and is helping lead the push for a "Green New Deal," have made it easier for progressives to stick to more collegial talking points. There are also more uncomfortable calculations to make in what is shaping up as a historically diverse field featuring a bumper crop of female candidates.

"There is a punishment or penalty women pay for being negative that is different from the penalty a man pays," Litman said. "That's not say that women don't do it -- of course they do -- but the framing and the action is very different and the way that it sounds or comes across is very different. So I think women will be more intentional about it."

Pete Buttigieg, the mayor of South Bend, Indiana, is, at 37 years old, the youngest candidate in the bunch -- a point he's underscored with his discussion of "intergenerational justice," a shorthand for broaching the difficulties, now being confronted by younger Americans, either created or exacerbated by their elders.

Still, he's been careful not be seen pitting one against the other.

"I think the trick for us," Buttigieg told The New Yorker, "is there should be a way to make a generational case without this all being about generational conflict. And I think there's a way to do it."

In an interview with CNN's Kate Bolduan, Buttigieg said he would not refer to the other candidates as "opponents." His preferred designation: "Competitors."

"When you're viewing others as opponents, you're looking to kind of find their weaknesses," he said. "When you're looking at competitors, you're thinking about how everybody brings something to the table. And I'm definitely the only left-handed, Maltese-American, Episcopalian, millennial, gay mayor in the race. So, you know, I've got that lane all to myself."

Even as they nod along to the current tune, Democrats with an eye on defeating Trump -- and desperate to mitigate any rifts that open up during the primary -- began drawing up insurance plans more than a year ago. The Democratic National Committee announced in 2018 that its 2020 convention would take place in mid-July, a few weeks earlier than in 2016 and more than a month ahead of when the 2008 edition was staged.

"My priority is to ensure that the 2020 nominating process is the most open, fair, transparent and inclusive in our party's history," DNC chair Tom Perez said in a statement last June. "That is exactly why the DNC has started this process (of scheduling the convention) early and before we have a full slate of candidates running for president. This will not only allow for a unified party but will ensure that our nominee is in the strongest position to take on Donald Trump or whoever the Republican nominee may be."

Swing Left, a Democratic group formed in 2017 that raised money for candidates to claim after they won their primaries, very purposefully stays out of the nominating contests. This year it established, along with the pundits at the liberal Crooked Media, what it's calling a "Unify or Die" fund for small dollar donors who want to give to the eventual nominee -- whoever it turns out to be.

"In the background of all this is 2016 and how people don't really feel like the Democratic Party got back together after the Hillary-Bernie primary," Ethan Todras-Whitehill, Swing Left's executive director, told CNN. "So, everyone is putting unity out there as a main message. It won't necessarily hold, but we think that having tentpoles like this will make it more likely to hold."