Storm heightens a sense of vulnerability to climate change.

Two days after the remnants of Hurricane Ida brought a sudden and ferocious storm to the Mid-Atlantic region, residents on Friday confronted the fallout from a downpour that killed at least 43 people across four states and illustrated with frightening clarity the threat posed by a changing climate.

In New Jersey, where at least 23 people were killed, many residents died in their cars, trapped by rapidly rising floodwaters and drowned without means of escape. In New York, at least 15 were dead, 13 in New York City, many of them submerged in ground-level apartments that they may have sought out for their affordability.

In Connecticut, a 26-year veteran of the state police force was killed when his car was swept away by floodwaters. And in Pennsylvania, at least four people died in counties close to the swollen Delaware River.

Destruction was widespread, from a row of homes in southern New Jersey leveled by a tornado that reached maximum wind speeds of 150 miles per hour, to cars submerged in water along the Sprain Brook Parkway in Yonkers.

The damage was all the more harrowing given that it came with relatively little warning from political leaders who were already contending with a pandemic that continues to kill thousands of Americans each week.

Those leaders, from President Biden down to New York’s Democratic nominee for mayor, Eric Adams, expressed a similar sentiment in their reactions to the storm: Climate change is here.

In a speech from the White House, Mr. Biden called the storm “devastating” before pivoting to discussion of the other natural disasters afflicting the United States, including wildfires in the West and the damage inflicted by Hurricane Ida in the South.

“This destruction is everywhere,” he said. “It’s a matter of life and death and we’re all in this together. This is one of the great challenges of our time.”

Gov. Kathy C. Hochul of New York, who assumed office a little more than a week before the storm hit, offered a similar message.

“It is not a future threat,” she said of climate change. “It is a current threat.”

And Mr. Adams, who is likely to become New York City’s next mayor, mixed his acknowledgment of the threat of the climate crisis with a sentiment that many New Yorkers shared, days after the rain stopped.

“I have never witnessed something like this,” he said.