MILWAUKEE (AP) — A Wisconsin congressman is calling President Donald Trump “a moron” over a tweet that urged global warming to “come back fast” in the face of dangerous cold hitting the Midwest.

Hundreds of schools in the region cancelled classes through Wednesday, and the governors of Wisconsin and Michigan declared states of emergency amid wind chills as low as negative 60 degrees (negative 51 Celsius).

Trump has frequently cast doubt on climate change, especially when cold weather hits. His tweet late Monday wondering “What the hell is going on with Global Warming” drew a quick response from Wisconsin Rep. Mark Pocan.

The Democrat responded by saying: “Only a moron would not understand global warming causes huge temperature swings.”

Northern Illinois University climate scientist Victor Gensini said the cold snap is “simply an extreme weather event” and doesn’t represent the global trend toward a warming Earth. He noted the record heat currently in Australia.