Sen. Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE (I-Vt.) on Sunday ripped President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE, saying he has failed to act appropriately as the leader of the United States or deliver on his campaign promises.

“What bothers me about this president is not so much what he says, although he is so offensive," Sanders said on ABC's "This Week with George Stephanopoulos.”

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"He talks about prison for his former opponent in a presidential election; this is not what presidents of the United States do," he added.

Sanders, who ran unsuccessfully against Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE in the 2016 Democratic presidential primary, said he is more concerned that the president is governing only on behalf of the wealthiest people in the country.

"I am more worried about what this president’s policies are in terms of telling the working people of this country during his campaign that he was going to stand with them," Sanders said.

"And yet he governs now as a representative of the billionaire class — tax breaks for the wealthy, cutting people off of health insurance, ignoring the needs of children, not dealing with the prescription drug crisis in this country that he said he was going to deal with," he added, describing Trump as "a pathological liar."

Sanders, however, avoided questioning the president's mental stability — a topic that has come up repeatedly this week after an explosive new book's release. The book, "Fire and Fury: Inside the Trump White House" by Michael Wolff, claims every White House aide is concerned about Trump's ability to lead the country.