LOS ANGELES—The sixth Democratic presidential debate started as a rerun of previous debates, featuring discussions of impeachment and the economy without any of the candidates disagreeing in any fundamental way. But it did mark one major departure from every preceding debate this cycle, by featuring the first substantive exchange about the dangers raised by climate change within the first half-hour of the event.

Climate change is, like impeachment and the economy, an issue where there is generally little daylight between the seven candidates on stage, but the subject rarely gets primetime placement in political debates, much less for a prolonged exchange.

“The issue now is whether we save the planet for our children and our grandchildren,” said Sen. Bernie Sanders (I-VT), calling for the country to declare a national climate emergency. “An American president—i.e., Bernie Sanders—can lead the world.”

“We’re the only country in the world that has taken great, great crises and turned them into an enormous opportunity,” said former Vice President Joe Biden. “We have to not rebuild to the standard that existed before… we have to rebuild to the standards that are existing today.

But the impact of all of those plans, said South Bend Mayor Pete Buttigieg,“is multiplied by zero unless something actually gets done.

“We cannot wait to act,” Sen. Amy Klobuchar of Minnesota said, quoting an Ojibwe saying that “great leaders make decisions not for this generation, but seven generations from now. This president doesn’t keep his decisions for seven minutes.”

Each candidate has put forward a climate plan emphasizing the criticality of getting the United States to net-zero carbon emissions by the middle of the century, and

“The biggest climate crisis we face is the politicians in Washington,” said Sen. Elizabeth Warren (D-MA). “America understands that we’ve got to make change and we’re running out of time… but getting Congress to act, you know, they just don’t want to hear it. If we don’t attack the corruption first, then were not going to be able to make the changes on climate, on gun safety, on all the big problems that exist.”

The exchange was groundbreaking in its content—a major, substantive conversation about the future of climate policy—but, like the 30 minutes of discussion about impeachment and the economy that preceded it, provided little opportunity for voters to see what set each candidate apart from the other. The result: As the impeachment saga continues to inhale the nation’s entire supply of political oxygen, the Democratic presidential contenders returned to the stage in slightly smaller numbers, but with almost no major change in the dynamics of the race.

According to the RealClearPolitics national polling averages, every candidate in the race is polling within the margin of error of where they were during the last presidential debate nearly a month ago. Biden still leads the field, his polling average rising and dipping as evenly and predictably as an EKG. Sens. Sanders and Warren are in a statistical dead heat, grasping for the support of the same wing of the party like those nature videos of eagles tumbling through the air while gripping each others’ talons. Buttigieg trails in fourth place, again, followed by the only fundamentally new player in the race, former New York City Mayor Michael Bloomberg, who, by dint of his decision to self-finance his campaign, is unable to qualify for the debate at all.

Due to the increasingly high polling hurdles placed before presidential hopefuls by the Democratic National Committee, the candidates doing the most interesting things weren’t even on the debate stage on Thursday: Hawaii congresswoman Tulsi Gabbard, fresh off her history-making “present” vote on articles of impeachment, failed to qualify, and declared last week that she wouldn’t attend even if she had; former Housing and Urban Development Secretary Julián Castro of Texas, who has lately framed his long-shot candidacy around the importance of reducing the importance of lily-white states like Iowa and New Hampshire in the nominating process, also failed to qualify.

So frozen is the campaign dynamic that even thinkpieces are starting to repeat themselves, the same narratives and attacks and concern-trolling (E.g.: “Medicare for All” is an expensive pipe dream; the DNC is rigging the system for the white moderates; Buttigieg is the wrong kind of gay) recycled again and again, like a pair of Toms Shoes crafted from a recycled pair of Toms Shoes.

Given that the last several debates are seen as having little effect on the fundamentals of the race for the nomination—Sen. Kamala Harris dropped out after the last debate, despite delivering something of a knockout punch to Gabbard—the man riding at the top of the polls indicated that his campaign sees no need to fix what, for him, ain’t broken. Speaking to reporters in an on-background meeting hours before the debate, senior Biden campaign officials indicated that the former vice president thinks it would be unhelpful for Democrats to spend three hours fighting with each other on stage.

Biden officials characterized Trump as Biden’s “opponent,” demoting his fellow Democrats to the rank of “competitors,” and indicated that the absence of Harris—the only candidate who has come close to toppling Biden’s place atop the field—had no effect on his debate prep.

The officials predicted that Biden’s main post-impeachment message would be that, despite all evidence to the contrary, uniting the country is not a lost cause—and that he is the candidate best positioned to do so.

For the other six candidates onstage, the reduced number of participants (seven versus the previous 10) and longer debate time (three hours versus two) may give them more breathing room to actually change the dynamic of the race—but if the opening was any indication, Thursday’s debate may end up being the Ghost of Christmas Future.

—with reporting by Matt Wilstein