Trump steps up claims, without evidence, that Biden aides illegally used autopen

He has ordered the Justice Department to investigate the claims Biden denies.

A day after ordering the Justice Department and White House to investigate former President Joe Biden's mental state while he was in office, President Donald Trump on Thursday doubled down on his accusations, without evidence, that Biden was not really running the country, claiming aides used his autopen to carry out "radical" policies.

Biden has denied the allegations and the Justice Department's legal counsel have endorsed autopens as lawful for signing bills into law, but Trump claimed during an Oval Office session with reporters that the use of the tool was the "biggest scandal maybe in the last 100 years" of this country.

Trump claimed he could tell which of Biden's executive orders were signed with an autopen and claimed aides used it to enact "open borders" and transgender rights policies he said Biden didn't support.

"He didn't have much of an idea what was going on. He shouldn't be ... I mean, essentially, whoever used the autopen was the president. And that is wrong. It's illegal, it's so bad and then it's so disrespectful to our country," Trump said.

Shortly after Trump directed the Justice Department to investigate "the circumstances surrounding Biden's supposed execution of numerous executive actions during his final years in office," Biden issued a statement to ABC News calling the probe "nothing more than a mere distraction."

"Let me be clear: I made the decisions during my presidency. I made the decisions about the pardons, executive orders, legislation, and proclamations. Any suggestion that I didn't is ridiculous and false," he said in his statement.

"This is nothing more than a distraction by Donald Trump and Congressional Republicans who are working to push disastrous legislation that would cut essential programs like Medicaid and raise costs on American families, all to pay for tax breaks for the ultra-wealthy and big corporations," Biden added.

Attorney General Pam Bondi has not directly addressed Trump's directive. A Justice Department spokesperson declined to comment when asked by ABC News.

Republican Sens. Eric Schmitt and John Cornyn will co-chair a Senate Judiciary Committee hearing this month about the allegations about Biden's mental state.

House Oversight Committee Chairman James Comer, a Kentucky Republican, issued a subpoena Thursday to Dr. Kevin O'Connor, Biden's physician, to appear for a deposition on June 27, as part what Comer said is an investigation into the cover-up of President Joe Biden's cognitive decline."

It's not clear whether O'Connor has responded.

When Trump was asked on what he based the accusations, he at first claimed that he didn't uncover any specific evidence that presidential documents were not signed by Biden.

"But I uncovered, you know, the human mind. I was in a debate with the human mind and I didn't think he knew what the hell he was doing," Trump said.

The president, however, claimed without details that "radical left, horrible people" worked around Biden without his knowing consent.

"I could give you the names of some of the people that use the autopen because I'm here and I ask questions about people that were here. Also, there are a lot of people that were here when that happened and they're here right now," Trump said without giving any further details.

"These were radical left lunatics that use that and they didn't get elected," he added before making a false claim that Biden was not elected.

ABC News' Alexander Mallin contributed to this report.