A nasty row that erupted between Hillary Clinton and Bernie Sanders over oil and gas industry donors last week is catapulting the issue of climate change into the race for the Democratic presidential nomination as it moves to New York, where an army of activists upstate is driven by opposition to drilling.

Mrs. Clinton has moved steadily left on the issue, under pressure from Mr. Sanders and his progressive allies, but she continues to come under assault, posing new challenges for her as the race moves to more liberal Northeastern states.

Last week, her mask of composure slipped when she angrily replied to a Greenpeace activist in Purchase, N.Y., “I am so sick of the Sanders campaign lying about me.”

Climate change is a powerful issue for voters in the Democratic base almost everywhere. But it has especially inspired grass-roots progressives in upstate New York, who fought — and won — a yearslong battle against fracking for natural gas.