WASHINGTON — With wildfires raging across the West, climate change took center stage in the race for the White House on Monday as former vice president Joe Biden called President Trump a “climate arsonist’’ while the president said that “I don’t think science knows’’ what is actually happening.

A day of dueling appearances laid out the stark differences between the two candidates, an incumbent president who has long scorned climate change as a hoax and rolled back environmental regulations and a challenger who has called for an aggressive campaign to curb the greenhouse gases blamed for increasingly extreme weather.

Trump flew to California after weeks of public silence about the flames that have forced hundreds of thousands of people from their homes, wiped out communities and forests, burned millions of acres, shrouded the region in smoke and left at least 26 people dead. But even when confronted by California’s governor and other state officials, the president insisted on attributing the crisis solely to poor forest management, not climate change.

Biden, for his part, assailed Trump’s record on the climate, asserting that the president’s inaction and denial had fed destruction, citing not just the current emergency on the West Coast but flooding in the Midwest and hurricanes along the Gulf Coast. In an outdoor speech at a museum in Wilmington, Delaware, the Democratic presidential nominee sought to paint a second Trump term as a danger to the nation’s suburbs, flipping an attack on him by the president.

“If we have four more years of Trump’s climate denial, how many suburbs will be burned in wildfires?’’ Biden asked. “How many suburban neighborhoods will have been flooded out? How many suburbs will have been blown away in superstorms? If you give a climate arsonist four more years in the White House, why would anyone be surprised if we have more of America ablaze?’’

The politicking came as firefighting teams across the West Coast battled shifting winds and drier weather Monday, sparking additional fire fronts that threatened to make new kindling out of forests and cover more of the country with hazardous smoke and falling ash.

Heavy smoke kept some firefighting aircraft grounded as fire pushed into new areas, prompting fresh evacuations in Idaho, Oregon, and California.

In Oregon, with a confirmed death toll of 10 along with 22 others missing, Governor Kate Brown said the state was getting firefighting support from as far as North Dakota and Michigan.

Doug Grafe, the chief of fire protection at the Oregon Department of Forestry, said crews had made progress containing fires. But he said rains anticipated to fall Monday were not materializing and winds threatened to exacerbate fire conditions in some areas.

Trump, who had come under intense criticism for barely addressing the crisis before, interrupted a western campaign swing to make a two-hour visit to an airport in McClellan Park outside Sacramento.

As soon as the president disembarked from the plane at Sacramento McClellan Airport, where the stench of smoke filled the air, he did not wait for his scheduled briefing to tell reporters that the cause of the conflagration was poor forest management, not climate change.

“When trees fall down after a short period of time, they become very dry — really like a matchstick,’’ Trump said. “And they can explode. Also leaves. When you have dried leaves on the ground, it’s just fuel for the fires.’’

At his subsequent briefing, however, Governor Gavin Newsom and his top environmental adviser pushed the president to acknowledge the role of climate change.

Newsom noted that only 3% of land in California is under state control while 57 percent is federal forest land, meaning under the president’s management as governed by federal law.

But he said climate change clearly was a factor. “Something’s happening to the plumbing of the world, and we come from a perspective, humbly, where we submit the science is in and observed evidence is self-evident that climate change is real, and that is exacerbating this.’’

Trump did not argue the point. “Absolutely,’’ he said, and then turned the floor over to another briefer.

But Wade Crowfoot, California’s secretary for natural resources, pressed Trump more bluntly.

“If we ignore that science and sort of put our head in the sand and think it’s all about vegetation management, we’re not going to succeed together protecting Californians,’’ he told the president.

This time, Trump rejected the premise. “It’ll start getting cooler,’’ he insisted. “You just watch.’’

“I wish science agreed with you,’’ Crowfoot replied.

“Well, I don’t think science knows, actually,’’ Trump retorted, maintaining a tense grin.