White House chief of staff Mark Meadows blasted Democratic presidential nominee Joe Biden for giving a "dark speech" at last week's Democratic convention, but was even more critical of his political record.

In an interview with "Fox News Sunday," Meadows claimed that Biden has done virtually nothing of substance in his decades in office, including his time as a senator and a vice president.

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"Joe Biden has barely passed two bills, one of which he’s trying to run away from because of the left," Meadows said, an apparent reference to a 1994 crime bill that he was behind. Biden has acknowledged during his campaign that the bill had its failures, but noted that it had support at the time.

"This president accomplished more in his first 100 days than Joe Biden did in the last 40 years," Meadows added.

Meadows also accused Biden of having a negative message at the convention.

"You couldn’t have watched any of that without considering it dark," he said, stating that the president would be more positive during the upcoming Republican convention.

Earlier in the interview, Meadows addressed a recent report of secretly recorded conversations the president's niece Mary Trump had with his sister, retired federal Judge Marianne Trump Barry. The recordings reportedly included Barry saying the president does not read and lacks principles.

“A number of the accusations that are being made I’ve been able to witness up close and personal and they’re just not true," Meadows said. "The president is not only well-prepared but reads so much that it causes me to have to read many times well into the night to catch up with him.”

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As for the criticism of the president's principles, Meadows said that Trump has already addressed this, but defended what he believed to be a key principle that the president has.

"I can tell you the principle that he has is that he loves this country, he’s proud of this country, he’s proud of the American people that actually make up this country," Meadows said, "and he’s willing to sacrifice everything, even the personal attacks that come each and every Sunday against this president.”

Meadows also addressed President Trump's claim that sheriffs and other law enforcement officials would be on hand at polling sites this November to keep order during the election. This drew criticism from House Speaker Nancy Pelosi, who accused Trump of trying to intimidate people to keep them from voting.

"I think what the president was really addressing was to make sure that if you want to show up and vote in person, we're going to make sure that that is safe," Meadows said. "To the extent that we're going to deploy thousands of sheriffs, no, we're not going to do that."

Lastly, Meadows addressed the group of conspiracy theorists known as QAnon, which has gained media attention in recent days, with the New York Times publishing a report claiming that some Republicans "embrace" it.

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"We don’t even know what it is," Meadows said, later adding, "We’re not going to address it, we're going to talk about things that are important."

White House Press Secretary Kayleigh McEnany told "America's Newsroom" Thursday that she has "never heard the president mention it."