The US House Speaker Nancy Pelosi unveiled a bill on Thursday that would establish a bipartisan congressional commission to evaluate a president’s fitness to serve under the 25th Amendment.

Iran Press/America: Pelosi told reporters that the commission will assess Donald Trump's capacity for carrying out his duties.

She insisted that the bill is not about President Trump, who has been treated for Covid-19 for the past week and is desperate to return to campaigning.

"He will face the judgment of the voters," the top Democrat said. "But he shows the need to create a process for future presidents."

Pelosi went on to say that the bill would establish a 16-member bipartisan panel of medical experts and former executive branch officials.

The panel would fulfill a process established under the US Constitution's 25th Amendment that was ratified in 1967, after John F Kennedy's assassination.

Pelosi said the move would preserve stability if a president suffers a crippling physical or mental problem, and provide guidance for the transfer of power to the vice president if needed.

Despite the proclamation that the bill is intended to address future presidents, Pelosi directly addressed Trump's health and how it has raised concerns.

"Clearly he is under medication. Any of us who is under medication of that seriousness is in an altered state," she told reporters.

"He has bragged about the medication that he has taken, and again, there are articles by medical professions saying this could... have an impact on the judgment."

Trump fired back angrily on Twitter and turned the issue against his election rival Joe Biden and running mate Kamala Harris.

"Crazy Nancy Pelosi is looking at the 25th Amendment in order to replace Joe Biden with Kamala Harris," Trump said.

"The Dems want that to happen fast because Sleepy Joe is out of it!!!"