“Courage is infectious.”

Trump went after Harris in a campaign-style rally on Tuesday marking his 100th day in office.

He mockingly called her a “phenomenal border czar” and an “exceptional candidate,” echoing some of the favorite lines he often used during his campaign.

Until Harris replaced Joe Biden atop the Democratic ticket last summer, Trump said, “I knew nothing about her.”

Harris warned Americans against perceiving Trump’s administration as merely disorderly, portraying it instead as a “fast-paced transformation,” a result of sustained efforts by the right to reshape government.

“A vessel is being used for the swift implementation of an agenda that has been decades in the making,” Harris said.

“An agenda to slash public education. An agenda to shrink government and then privatise its services. All while giving tax breaks to the wealthiest among us.”

Harris chose a friendly audience for her return to the political arena, addressing the 20th anniversary gala for Emerge America, an organisation that recruits and trains Democratic women to run for office.

It grew in part from Harris’ run for San Francisco district attorney in the early 2000s.

The speech was delivered below luminous chandeliers in a gold-trimmed ballroom in the landmark Palace Hotel.

Harris is ramping up her public presence as Democrats nationally search for a path forward after November’s election, in which Republicans also won control of Congress.

While a slate of high-profile Democrats — from governors to businessmen — seek leadership roles within the party, the former vice president retains unique influence and would reshape any future race she chooses to enter.

She praised Democrats who have been especially prolific in criticising Trump, name-dropping lawmakers diverse in their ideology and style: senators Cory Booker, Chris Van Hollen, Chris Murphy and Bernie Sanders along with representatives Jasmine Crockett, Maxwell Frost and Alexandria Ocasio-Cortez.

But she did not take a stand in one of her party’s central divides, neither calling for mass mobilisation like Illinois Governor JB Pritzker or questioning Democratic positioning on key issues like California Governor Gavin Newsom.

“I’m not here tonight to offer all the answers,” Harris said. “But I am here to say this: You are not alone and we are all in this together.”

But she warned that things will probably get worse before they get better.

“The one check, the one balance, the one power that must not fail is the voice of the people,” she said.

Harris, a former state attorney general and US senator from California, has not discouraged speculation that she might enter the race to replace the term-limited Newsom, himself a potential contender for president.

And she has not ruled out another run for the White House.

She did not address her future Wednesday.

She continues to fundraise, using a joint committee that includes Harris for President, the Democratic National Committee and state Democratic parties.

The committee, the Harris Victory Fund, reported having about $US4.5 million ($7 million) on hand at the end of March, according to federal records.

In recent fundraising emails, Harris has been blunt about the need for Democrats to unify ahead of the 2026 midterm elections.

Democrats need to “organise and stop Trump’s agenda while electing Democrats everywhere,” she wrote in recent emails.

“There has never been a more important time for a strong Democratic Party — one that is willing to stand up to Donald Trump, Elon Musk and what they are doing to this country.”

The event marks a homecoming of sorts.

Harris lives in Los Angeles but she is from the San Francisco Bay Area, where her political career is rooted.

For her first major speech since the election, she chose familiar terrain and a friendly, in some ways familial, crowd.

Lisa Gotbhi, a health care executive in San Francisco, said Harris’ loss last year was a “shock”, but “she’s a voice we need and a leader we need. Let’s get back in the fight”.