For the first 100 days of President Trump’s new term, Kamala Harris drifted into the recesses of political defeat back home in Los Angeles. She mulled her thoughts and pondered whether to run for California governor but, noticeably, said little about the president.

It wasn’t until Wednesday night that the former vice president waded back into the conversation with an affirmation of Democratic frustrations, in a speech that her camp had billed as her most extensive remarks since leaving Washington after losing her bid for the White House.

The nation, she warned, was at risk of a constitutional crisis if the courts and Congress fail to stand up to the president — or if the president defies them nonetheless.

“That is a crisis that will eventually impact everyone,” she said. “Because it would mean that the rules that protect our fundamental rights and freedoms, that ensure each of us has a say in how our government works, will no longer matter.”

Ms. Harris’s 16-minute address covered the familiar ground that other Democrats have sounded the alarm about for months. She was in the friendly confines of San Francisco, where she launched her political career as district attorney more than two decades ago, speaking to an organization that lifts up Democratic women running for office.

“It’s wonderful to be home,” Ms. Harris said as she began her speech beneath the chandeliers of a hotel ballroom.