One of the most illuminating moments in the Republican debate came 20 minutes in. The reaction to it was swift and - among some young people and scientists - angry.
Did humans contribute to climate change? That was the question from the Fox News moderators to the eight presidential hopefuls on stage.
After reading out some statistics from the deadly Hawaii wildfires, they played a clip from a member of the Young Americans for Freedom, a conservative youth activist organisation, who said climate was the number one issue for young people.
Asked to raise their hand if they thought mankind was to blame, Florida Governor Ron DeSantis interjected to say a show of hands was childish. Instead he laid into Joe Biden for the president's response to Hawaii. .
Only one candidate said climate change was real in the short discussion that followed.
Former UN ambassador Nikki Haley went the furthest in agreeing with the question by saying: "Is climate change real? Yes it is."
It was up to China and India to lower emissions, she said.
Cutting the US carbon footprint has been costly to the economy and put the country at a disadvantage globally, said Tim Scott. The South Carolina senator said bringing jobs "home from China" would help ease that pain and improve the environment.
One Republican candidate said the climate change agenda was a hoax.
"The reality is that the anti-carbon agenda is the wet blanket on our economy," said Vivek Ramaswamy, a biotech millionaire and the youngest candidate in the field. "More people are dying of bad climate change policies than they are of actual climate change."
Boos followed. But as he prefaced his remark by saying he was the only one on stage not "bought and paid for", it was unclear what the audience was responding to.
Instead of answering the climate question, Chris Christie turned his fire on Mr Ramaswamy, calling him a "guy who sounds like a ChatGPT" and the discussion descended into chaos.
Donald Trump, who chose not to attend, has in the past minimised the threat of climate change by joking about oceans rising by one hundredth of an inch over 300 years. As president, he pulled out of the Paris climate accord.
The issue has become more talked about as extreme weather has caused havoc in the US. More than 100 people were killed on the Hawaiian island of Maui by wildfires and hundreds more remain missing, while California has been battered by its first tropical storm in 80 years.
The American Conservation Coalition, which mobilises young people around environmental action, condemned what they heard on stage in Milwaukee. Challenging Mr Ramaswamy directly, they said: "No, climate change is not a hoax. Candidates with this thinking are completely out of touch with young conservatives."
They then thanked Mrs Haley for being the only person on stage "bold enough to tackle climate change head-on".
The Sunrise Movement, a youth activist group which campaigns on climate change, said: "Vivek calls climate change a hoax. We call bluff that he's been outside this summer."
This year has already seen the hottest day ever recorded, the hottest month and - very likely - will also become the hottest year on record.
The science is clear-cut - the world's rising temperatures are the result of man-made climate change.
So it is perhaps not surprising that many climate scientists reacted with dismay at the opinions expressed during the Republican debate.
Corinne Le Quere, professor of climate change science at the University of East Anglia was unambiguous - humans are causing climate change.
"This is not a political issue, it is a scientific fact that stems from overwhelming evidence from observed climate and from understanding the Earth's physical processes."
Professor Ed Hawkins, a climatologist at the University of Reading, agreed that whether humans are causing climate change is not a matter of belief. "It is a scientific fact, endorsed by the climate science community, learned societies and every government around the world," he said.
"How to respond to that fact is certainly a matter for political debate, and that is where the focus needs to be," he continued.
The climatologist Professor Michael E Mann of the University of Pennsylvania was more pungent. The Republican Party "is not just a threat to the nation. It is a threat to the planet", he said on X, formerly known as Twitter.
Meanwhile the meteorologist Eric Holthaus posted "Climate denial is alive and well in the year 2023."