Ms Pelosi’s statement came just before congressional Democrats began a conference call to discuss whether to impeach Mr Trump for an unprecedented second time, two days after his supporters — inflamed by his false claims of election fraud — stormed the US Capitol, smashing windows, sending lawmakers into hiding and leaving five dead.
“The situation of this unhinged President could not be more dangerous,” Ms Pelosi said. The House of Representatives speaker said she had discussed the matter with Army General Mark Milley, the chairman of the Joint Chiefs of Staff.
While US presidents have access to the codes needed to fire nuclear weapons 24 hours a day, no top military or national security official has expressed any concern publicly about Mr Trump’s mental state with regard to nuclear weapons.
Milley’s office said that Ms Pelosi had initiated the call and that the general “answered her questions regarding the process of nuclear command authority”.
A US official, speaking on the condition of anonymity, said that any use of nuclear weapons is a highly deliberative process.
In opening the conference call, Ms Pelosi called Mr Trump “an insurrectionist” and said the members were there to discuss “how we go forward,” according to a source on the call.
A day after an uncharacteristically subdued Mr Trump promised in a video to ensure a smooth transition to President-elect Joe Biden’s administration, he returned to a more pugilistic tone.
On Twitter, he praised his supporters and said, “They will not be disrespected or treated unfairly in any way, shape or form!!!”
Mr Trump also confirmed he would not attend Mr Biden’s January 20th inauguration, departing from a time-honored tradition that typically sees the outgoing president escorting his successor to Capitol Hill for the ceremony. The practice is seen as an important part of the peaceful transfer of power.
At least one Senate Republican, Ben Sasse of Nebraska, said he would consider supporting an impeachment proceeding.
Sasse, a frequent Mr Trump critic, told CBS News on Friday he would “definitely consider” any articles of impeachment because the president “disregarded his oath of office”.
Even if the House impeaches Mr Trump at such short notice, the decision on whether to remove him would fall to the Republican-controlled Senate, which has already acquitted him once before. With Mr Trump’s term ending in 12 days and the Senate scheduled to be in recess until the day before, the prospects of an actual ouster appear unlikely.
Removing a US president requires a two-thirds majority in the Senate. Republican Senate Majority Leader Mitch McConnell has not commented on a possible impeachment.