Vice president Kamala Harris told Republicans to “bring it on” in what she described as a “fight for our most fundamental freedoms” as she spoke to the American Federation of Teachers.

It was her latest stop in her whirlwind debut as the Democrats’ likely presidential nominee after President Joe Biden abruptly dropped his bid for a second term at the beginning of the week.

Ms Harris praised unions as the foundation of the middle class, and she criticised Republicans for their views on gun control and public education.

“They have the nerve to tell teachers to strap on a gun in the classroom while they refuse to pass common sense gun safety laws,” she said.

Ms Harris added that “we want to ban assault weapons, and they want to ban books”.

The American Federation of Teachers was the first labour union to formally endorse Ms Harris, and its president Randi Weingarten said she “has electrified this race”.

Ms Harris intends to travel aggressively to spread her message and rally voters.

The outreach occurs as the retooled Biden campaign, now under Ms Harris’ control, figures out its strategy for generating turnout and maximising her time in a 100-plus day sprint to the November election against Republican Donald Trump.

In Mr Trump, Ms Harris is up against the survivor of a recent assassination attempt with tens of millions of loyalists committed to returning him to the Oval Office.

Just as Ms Harris is trying to draw a contrast with Mr Trump, he is working to do the same with her.

Mr Trump went on the offensive at a rally on Wednesday in North Carolina, calling Ms Harris a “real liberal” who is “much worse” than Mr Biden.

The former president claimed without evidence that Ms Harris had misled voters about the health of the 81-year-old Mr Biden and his ability to run for the presidency.

Ms Harris’ appearance at the teachers union’s biennial convention in Houston follows a rally on Tuesday in the Milwaukee area and a speech on Wednesday to a gathering of the historically black sorority Zeta Phi Beta in Indianapolis.

“We know when we organise, mountains move,” she told sorority members. “When we mobilise, nations change. And when we vote, we make history.”

Her campaign is seizing on the growing pop culture interest surrounding her candidacy, releasing a video on Thursday that is set to Beyonce’s Freedom.

The video, designed for social media consumption, underscores a core message of Harris campaign – freedom on abortion rights, freedom from gun violence and freedom “not just to get by, but to get ahead”.

The 1.8 million-member AFT has backed Ms Harris and her pro-union agenda on the premise that a second Trump term could result in restrictions on organised labour and a potential loss of funding for education.