Hillary Clinton on Tuesday sharply questioned President Trump’s conduct in office, criticizing his foreign policy pronouncements and penchant for posting on Twitter, and described herself as “part of the resistance.”

During an interview with the CNN correspondent Christiane Amanpour, Mrs. Clinton, who has kept a relatively low profile since her defeat in the presidential race, repeatedly characterized Mr. Trump as struggling in the presidency. The interview was at an event hosted by Women for Women International, a nonprofit group, in Midtown Manhattan.

Mrs. Clinton voiced disbelief at what she cast as the White House’s slapdash approach to issues like health care and the North Korean nuclear program.

She repeatedly said that Mr. Trump did little to prepare for the presidency. And but for the actions of Russian-backed hackers and the F.B.I. in late October, Mrs. Clinton said, she would have won.