MANCHESTER, N.H. – Democratic presidential candidate Tom Steyer accused nomination rival Pete Buttigieg on Monday of not being aggressive enough on the issue of climate change.

Steyer, speaking with reporters while campaigning in New Hampshire, was asked a question by Fox News about another rival – Sen. Elizabeth Warren of Massachusetts. But he quickly pivoted to the South Bend, Ind., mayor who was a popular target at last week's primary debate – saying “to me the question, which I asked Pete Buttigieg on the stage, is why don’t you have a better climate stance?”

“'You're 37 years old. You know, you're of a generation of people who understand this is the number one issue in front of us. Why aren't you stronger on climate?’ That to me is an absolutely critical question for him to answer,” the 62-year-old hedge fund manager turned billionaire environmental advocate said.

Steyer, whose signature issue is climate change, was referring to his jab at Buttigieg at last Thursday’s Democratic presidential primary debate.

Steyer – who vows to “declare a state of emergency on day one” regarding climate change if he wins the White House – was outlining the steps he’d take to combat the global crisis when he turned to Buttigieg and said: “I would call on Mayor Buttigieg to prioritize this higher because the people in his generation understand that this is a crisis that we have to go on right now but it’s also the greatest opportunity to rebuild and re-invent America.”

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Buttigieg – who along with Vice President Joe Biden, Sen. Bernie Sanders of Vermont, and Warren is considered part of the top-tier of four candidates – answered: “I’ve made clear that this will be a topic of day one action,” before delving into specifics of the plan he's unveiled to tackle climate change.

Steyer has repeatedly touted that climate change is “my number one priority” and highlights that “I don’t think there’s anyone else running for president who will say that.”

Asked by Fox News if he was satisfied with Buttigieg’s answer on the debate stage last week, Steyer said: “No. I don’t think so. I don’t think he responded to it directly at all. I think that’s a fact.”