Tucker Carlson said Tuesday that Sen. Bernie Sanders, I-Vt., has proven himself to be a "professional loser" and more focused on being ideologically "pure" than politically successful.

The "Tucker Carlson Tonight" host said that Sanders had shown he was unwilling to go all-out for the Democratic nomination by refusing to directly criticize rival Joe Biden's many gaffes and missteps or question his "mental acuity."

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Carlson noted that Sen. Cory Booker, D-N.J., who endorsed Biden Monday, wasn't apprehensive about calling out Biden during a 2019 debate.

"So according to Bernie Sanders, we are not allowed to talk about the one thing all of us can see clearly every day: The Democratic front-runner is failing," Carlson said. "He's not capable of taking the job he's running for."

"It is pretty obvious Sanders doesn't want to win -- He's a man who thinks it's more noble to fail than to succeed," the host continued. "You're watching a professional loser. Sanders is all but admitting that now, and already promised to back Biden if Biden wins the nomination. And he has even pledged not to contest the convention if Biden falls short of a delegate majority."

Carlson explained that if Sanders was a true "revolutionary," he wouldn't cut deals or back down if he is losing.

"Real revolutionaries go to the wall for what they believe," he said. "Bernie Sanders won't even go to the convention. Because that is who Bernie Sanders is and that's who he has always been."

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Carlson added that Sanders proved this habit of submission at a 2015 rally in Washington state, where two protesters came on stage and took the microphone away. Sanders stood aside, and later ended the rally early.

"Imagine doing that yourself. Imagine how much self-loathing you would have," Carlson said, adding that Sanders reportedly admonished one of his own supporters for criticizing Biden as a corrupt politician.

The host said Biden proved himself in the Senate to be a "paid lackey of credit card companies" -- an apparent reference to the Delaware lawmaker's relationship with top figures at the former Wilmington-based MBNA, which has since been purchased by Bank of America.