Washington DC - President Joe Biden has shied away from harshly attacking Donald Trump on the national stage, but reportedly, behind closed doors is a much different story.

In a recent report from Politico, several sources told the outlet that they personally witnessed Biden describe Trump as a "'sick f**k' who delights in others' misfortunes" to some of his longtime friends and closest aides.

For the most part, Biden has avoided seriously blasting his challenger in public, even as Trump faces 91 criminal charges which may threaten his re-election effort.

His harshest criticisms of Trump have come amid the launch of his reelection campaign, having called the former president a "loser" while giving a speech in South Carolina and comparing his rhetoric to "language used in Nazi Germany" at a rally in Pennslyvania.

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Trump, on the other hand, has regularly used his rallies to insult other politicians and officials, spread misinformation and conspiracy theories, and call on his base to enact political violence.

In response to the president's remarks, senior Trump campaign advisor Chris Lacivita said, "It's a shame that Crooked Joe Biden disrespects the presidency, both publicly and privately.

But then again," he added, "it's no surprise he disrespects the 45th president the same way he disrespects the American people with his failed policies."