Joe Biden's fellow Democrats are trying to bring him down because he's "too conservative," according to Washington Post columnist Marc Thiessen.

The Fox News contributor told "America's Newsroom" Wednesday morning that he's worked extensively with Biden on Capitol Hill and is shocked by the methods taken by Democrats to discredit the 2020 presidential hopeful.

"They want to bring him down. That's not surprising," Thiessen said. "What is surprising is how they'll try to bring him down, arguing that he is too conservative. That's the state we've gotten to in the modern Democratic party.

"The Obama/Biden approach to governing is no longer acceptable for the Democratic socialist trying to take over the nominating process and government," he continued.

BIDEN 'ABSOLUTELY AGREES' WITH WOMAN WHO BLASTS TRUMP PRESIDENCY BY CALLING IT 'ILLEGITIMATE'

Biden faced criticism this week over comments he made about climate change and his prediction that Republicans would experience an "epiphany" about working with Democrats after President Trump leaves office.

Fellow 2020 presidential candidate Bernie Sanders and Rep. Alexandria Ocasio-Cortez slammed Biden's "middle ground" approach to climate change during a rally on Monday in support of the Green New Deal.

"They want a Green New Deal. Anything less is heresy," Thiessen said of Democrats' behavior.

"They want government health care for all whether you want it or not, and say Biden is too moderate. He is not moderate. He is a liberal Democrat," he continued.

BIDEN DEFENDS HIS CLIMATE CHANGE RECORD AMID CRITICISM FROM OCASIO CORTEZ, TELLS CRITICS TO 'CALM DOWN'

In response to Biden's "epiphany" comments, Thiessen said the former vice president has the support of most Democrats in shifting to a more moderate stance and finding common ground with Republican officials, but that some detractors see Biden as an "obstacle to the goal of socialism."

"His big heresy is that he wants to work with Republicans and come up with bipartisan solutions," Thiessen said. "It's not acceptable in the age of the resistance.

CLICK HERE TO GET THE FOX NEWS APP

"The resistance doesn't want to work with Republicans. They don't want compromise. They aren't just opposed to Donald Trump. They're composed to conservatism, compromise and the free enterprise system as it exists today and they want to fundamentally change America," he concluded.