Houston, Texas - Kamala Harris launched a blistering attack on Donald Trump and his "extremist" Republicans as she addressed teachers Thursday, seeking to rally a key part of the Democratic coalition behind her bid to take on the billionaire for the presidency.

Harris – the country's first female vice president and seeking to make history again in November – has enjoyed a groundswell of support from labor groups, ethnic minorities, and her own party since announcing her 11th-hour candidacy to replace President Joe Biden as the candidate.

The first union to endorse her, the American Federation of Teachers, applauded at their convention in Houston as Harris warned that America was witnessing a "full-on attack" by Trump's Republicans on "hard-won, hard-fought freedoms."

"While you teach students about democracy and representative government, extremists attack the sacred freedom to vote. While you try to create safe and welcoming places where our children can learn, extremists attack our freedom to live safe from gun violence," she said.

Donald Trump Trump sounds dark tone at rally as Kamala Harris says she's "ready" for debate

"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."

Harris (59) jumped into the election after weeks of turmoil over 81-year-old Biden, who bowed out Sunday after a dismal debate performance against Trump accelerated concerns over his mental capacity and persistently low polling numbers.

Calling herself "a proud product of public education," she connected her personal story to her political outlook, telling her audience that the work of teaching was "personal and it is professional, and... so critically important."

The former top prosecutor for California tied the event to a key campaign message about refusing to go back to Trump's America, praising her audience as "visionaries" who look to the future.

"You see the potential in every child. You foster it, you encourage it, and in so doing, you shape the future of our nation, which is why I say we need you so desperately right now today," she said.

She contrasted Democratic efforts to cancel student debt and her vision of investment in public schools and universities with Trump's vow to dismantle the Education Department and cut spending in half.