Washington DC - President Donald Trump went on a wild tangent while hosting Germany's newly-elected Chancellor Friedrich Merz at the Oval Office, showcasing a growing obsession with his predecessor's use of autopen.

In the middle of a discussion about Russia's war on Ukraine, Trump abruptly switched topic and started ranting about Biden's use of autopen, a device used by presidents for decades to reproduce their signatures.

"Did somebody say autopen?" he asked, before launching into his tirade. "Did I hear the word autopen? I'm just curious because I think it‘s the biggest scandal maybe in the last 100 years in this country."

Trump this week said he directed the Department of Justice to launch an investigation into Biden's cognitive decline and the potential use of autopen by other members of his administration.

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The memorandum rails about "one of the most dangerous and concerning scandals in American history" and claims the public was "purposefully shielded from discovering who wielded the executive power."

"Well, look the autopen I think is the big scandal – outside the rigged election of 2020 – I think the biggest scandal of the last many years," Trump continued Thursday.

He said that he could tell when a signature was made with an autopen, citing "two little pinholes" and even roped Merz into the discussion.

"Yep," the German leader responded awkwardly.

"I think it's very disrespectful to people when they get an autopen signature," Trump said.

"I don't think he had any idea what was... he didn't have much of an idea what was going on."