While the Senate spent much of the day Tuesday sparring over the rules governing the impeachment trial of President Trump, Tucker Carlson focused on the man at the heart of the investigation, former Vice President Joe Biden, and his simmering feud with Sen. Bernie Sanders l-Vt.

"Somehow Bernie Sanders is apologizing for the crime of telling the truth about Joe Biden," Carlson said on "Tucker Carlson Tonight."

SANDERS APOLOGIZES TO BIDEN OVER UNOFFICIAL SURROGATE'S BLISTERING OP-ED

Late Monday, Sanders apologized to Biden over a blistering op-ed written by an unofficial campaign surrogate, who blasted the former vice president as a weak candidate with a serious corruption problem.

"The entire Democratic establishment landed on Bernie Sanders with both feet. Sanders got the message: Apologize or we will destroy your candidacy," Carlson said, adding that in response, Sanders "promptly groveled for mercy."

Fordham University School of Law professor Zephyr Teachout wrote in a column published by The Guardian that while Biden was happy to be called "Middle-Class Joe," he has a long history of supporting "finance over working-class Americans."

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Teachout wrote that nominating a candidate like Biden would make it more difficult for Democrats to defeat Trump in November, since it would allow the president to "muddy the water, to once again pretend he is the one 'draining the swamp.'" She also wrote that Biden’s record illustrates the "grossly corrupt culture in Washington that long precedes Trump."

Sanders distanced himself from the op-ed, telling CBS News Monday: "It is absolutely not my view that Joe is corrupt in any way. And I'm sorry that that op-ed appeared."

Carlson said Sanders' apology reminded him of a "hostage tape filmed under duress."

"What's happening here? Simple," he added."The self-sustaining organism that is the Democratic establishment is dumping antibodies into the system to protect itself. Bernie Sanders, like Donald Trump, is a threat to their power. Joe Biden is not a threat to their power."

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"It's like they care about Joe Biden as a person," Carlson continued. "If they cared about Joe Biden, they would've convinced him not to run. Biden is in no condition to be president or even to run, as you've noticed. He is humiliating himself and his family. For now, Biden is all they've got."

Carlson said that if Hillary Clinton or former first lady Michelle Obama were to belatedly jump into the race, "Biden will be tossed aside and forgotten."

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"They [candidates] are vessels for temporary use. What the left cares about is regaining control of the country," he concluded. "That's why they will do whatever's necessary to protect Joe Biden for now as long as it's necessary."

Biden accepted Sanders' apology via Twitter Monday and urged the remaining candidates to keep their focus on making Trump a one-term president.

Fox News' Edmund DeMarche contributed to this report.