The speaker has long resisted calls from many progressive lawmakers to initiate impeachment proceedings against the president, but Democrats appear to have reached a breaking point over the administration's refusal to hand over a whistleblower complaint related to Mr. Trump's interaction with a foreign leader.
"This week, the president has admitted to asking the president of Ukraine to take actions which would benefit him politically," Pelosi said. "The actions of the Trump presidency revealed dishonorable facts of the president's betrayal of his oath of office, betrayal of national security and betrayal of the integrity of our elections."
The current furor stems from a call Mr. Trump made to the president of Ukraine in July, in which he admitted discussing Joe Biden in the context of fighting "corruption" in the country. Mr. Trump and his allies, in particular personal attorney Rudy Giuliani, have accused Biden of pushing for the ouster of a Ukrainian prosecutor while he was vice president in order to benefit his son. The prosecutor was widely seen as corrupt, and no evidence of wrongdoing by Biden has emerged.