ATLANTA — They're playing not to lose.

The top four candidates for the Democratic presidential nomination barely even sparred with one another at a 10-person MSNBC/Washington Post debate at Tyler Perry's sprawling studio complex here Wednesday night.

Without a doubt, the incentive structures and circumstances were a bit different for each member of the breakaway group — former Vice President Joe Biden, Massachusetts Sen. Elizabeth Warren, Vermont Sen. Bernie Sanders and South Bend, Indiana, Mayor Pete Buttigieg — but they all added up to taking a lap under a caution flag in a race in which many candidates have failed but no one has taken a commanding lead.

Download the NBC News app for breaking news and politics

The others had little reason to go after Buttigieg, who has struggled with black voters across the country at the same time he's risen to the top of the polls in the Iowa caucuses, according to Howard Franklin, an Atlanta-based Democratic strategist.

"He is already lacking support from the constituency that could propel him deep into the primary — black voters," Franklin said. "His connection to other segments of the electorate is strong and authentic, so there's little upside in picking at his sore spot or attacking from a new, likely ineffective angle."

There's also risk, Franklin added: "Mayor Pete has also cultivated the 'nice guy' persona in the race, and his highly educated base of voters would likely remember and resent a public broadside, possibly withholding their support from the attacker [later], even if the criticism rang true."

According to NBC's tracker, Biden leveled one attack at Warren and one at Sanders; Buttigieg knocked Warren once; Sanders hit Biden once; and Warren went after Trump, the "ultra-rich" and corporations — but none of her Democratic opponents.

For Biden, who has shown resilience as the front-runner in the race since he entered it seven months ago, there's enough to worry about in terms of not tripping over his own words that delivering attacks on other candidates might be a risky proposition. And, at the same time, sentiment about him in the Democratic Party is so positive that he has proven to be a sympathetic figure when under fire from others.

That means his rivals know they swing at their own peril.

For Warren, the reluctance isn't just situational but in line with a strategy built around focusing on her own vision rather than what her opponents are saying.

"It's largely been Warren's plan" not to fight with other Democrats on stage, said Christina Reynolds, a senior aide on Hillary Clinton's 2016 presidential campaign, who noted that this contest featured lines of questioning on issues such as housing and abortion that haven't received much attention in previous debates this year. "They used that opportunity to pitch their own plans and contrast with Trump more than each other, which, as a Democrat, I’m OK with."

For months, Democratic strategists have said that the party's voters aren't interested in seeing internecine warfare at a time when they are unified in their disdain for both President Donald Trump's policies and his bombastic attacks on a wide variety of Americans.

The cautionary tale on that score has been Sen. Kamala Harris, D-Calif., whose earlier scraps with Biden fueled a temporary bump in her polling but may also have turned some persuadable voters away from her campaign more permanently.

On Wednesday, Harris pointedly passed up an opportunity to take Buttigieg to task when she was asked about his campaign using an image of a Kenyan woman in association with its plan for improving the lives of black Americans.

"I believe the mayor's apologized for that," Harris said, turning the question to the "larger issue" of white candidates relying on black voters to help them win elections and then not returning to black communities to deliver on policy once elected.

"Show up for me," she said.

And while one of the lower-ranked candidates, Rep. Tulsi Gabbard of Hawaii, did fire off several rounds of volleys at fellow Democrats, there was also a top-tier contender who may have wanted to mix it up a little more.

Sanders was ready to go toe-to-toe with other leading candidates, according to his campaign manager, Faiz Shakir, said.

"I don’t think there’s any unwillingness to engage," he said, adding that he believed the format didn't allow for enough direct exchange between the competitors. "There’s just not opportunity to do so unless you really have to just speak over everybody and say, ‘Hey, you know,’ insert yourself and say, ‘Stop talking everybody, I want to engage Mayor Buttigieg.' It just didn’t allow for it.

Asked whether that means Sanders will be looking to strike at the next debate, Shakir said, "I'll hold and reserve that."