Bernie Sanders thinks President-elect Donald Trump is a "pathological liar."

The senator from Vermont and former Democratic presidential candidate appeared on MSNBC's "All In with Chris Hayes" on Thursday night, characterizing Trump as inconsistent and unpredictable.

Sanders said the looming Trump presidency presents Americans with a uniquely challenging future and said Americans need "to build a movement of millions of people who actually are following reality."

"That's the challenge," he added.

"Real change in this country, I am more and more convinced of it, is not going to come from Capitol Hill. It's going to come from grassroots America."

Sanders' comments appear to suggest Trump has not kept his campaign and post-election promises to "drain the swamp in Washington," to rid the government of insiders who wield too much influence.

Instead, Trump has filled his Cabinet with billionaires, Wall Street bankers, and establishment figures.

Watch Bernie Sanders' comments below: