"This occupant of the Oval Office poses a clear and present danger to our future and to our democracy," Clinton said at the NARAL event that included U.S. House Speaker Nancy Pelosi.
"In the course of his duties as our president, he's endangered us all by putting his personal and political interest ahead of the interest of the American people so this is a moment of reckoning," Clinton added.
Trump now faces impeachment after a whistleblower's complaint that has led the U.S. House of Representatives to open an impeachment inquiry which accuses White House officials of trying to conceal "politically sensitive" information about Trump's July 25 phone call with Ukrainian President Voldymyr Zelenskiy by moving it to one of the government's most sensitive computer systems.
The whistleblower, in the complaint made public on Thursday, said White House lawyers directed officials to remove the call summary from the classified computer system, or server, where the administration normally stores those records to try to "lock down" access to the information.
Transcripts of president's phone calls are normally stored on a classified White House computer system accessible to "at most, a low double-digit number of people," said Larry Pfeiffer, director of the Michael V. Hayden Center for Intelligence, Policy and International Security in Virginia.
Moving the transcript to an even more restrictive system - one normally used to store information about specially sensitive government secrets - would be "unusual given the contents of that call," he said.
The White House did not respond to a request for comment about this story. Reuters was unable to corroborate the allegations about the server.
Under pressure after news of the whistleblower's complaint emerged in media reports, the White House on Wednesday released the call summary. The House Intelligence Committee demanded the complaint and on Thursday released it to the public.
The whistleblower's accusation opens up a potential line of attack by his political opponents on the campaign trail.
Trump hammered Clinton during the 2016 campaign for her use of a private server to store sensitive government emails. The FBI investigated whether Clinton had mishandled classified materials and recommended against charging her with a crime despite concluding there was classified information among the emails she sent and received.
Clinton has denied sending or receiving classified information on her unsecured private email account. Longtime Clinton spokesman Nick Merrill said on Thursday that "in a land of ironies this reigns king."
Trump has dismissed the whistleblower complaint as a "partisan hack job."