WASHINGTON — Maxine Waters runs around the U.S. Capitol these days — moving fast in heels as she balances back-to-back television interviews, speeches, hearings and hugs from millennials who have called her “Auntie Maxine” to celebrate her outspoken style.

It is an odd new celebrity for a 78-year-old Washington fixture who has logged more than 25 years in the House, representing Los Angeles, from gritty but gentrifying Inglewood to largely white, working-class Torrance. But in President Trump, her sharp tongue has found its perfect target, and Auntie Maxine has gone viral.

“Trump was just so outrageous, so disrespectful, such a bully and dangerous for this country, I decided, ‘You know what? I’m taking the gloves off and I’m going to step out,’” Ms. Waters said. “I was going to not only challenge him but encourage others to see him for what he is: basically a bully, an egotistical maniac, a liar and someone who did not need to be president.”

Ms. Waters never seems to tire of pressing this case. She has labeled Mr. Trump a “disgusting, poor excuse of a man.” She has called Mr. Trump and his associates “the Kremlin Klan” and began calling for his impeachment soon after he took office.