The Democrat nominee hopeful made the post, which has now been shared thousands of times and liked by nearly 200,000 accounts. Mr Sanders and Trump have been fierce rivals in recent years and have different views on climate change. But in the simple tweet, Mr Sanders wrote: “Donald Trump believes climate change is a hoax.
“Donald Trump is an idiot.”
His comments however sparked fury among Republican supporters.
One wrote: “You are a complete moron Bernie Sanders – speaking as one who has an environment degree.”
Another said: “I wish other politicians wouldn’t stoop to name calling. Yes hes an idiot but lets try to be tactful.
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“Trump has ruined the way our people talk.
“Thats the biggest thing I will remember about him. He has made it ok to openly sling mud at people.”
A third added: “The democrats playing the scare tactics with climate change & putting the deadline of 12 years is greater hoax.
“The biblical false prophets.”
Mr Sanders is running to become President in 2020.
He first needs to secure the support of his Democrats party.
He would then take on Trump in a head-to-head battle for the White House.
Trump is widely expected to be the Republican candidate.