President Donald Trump said Wednesday that he was vetoing the National Defense Authorization Act for Fiscal Year 2021.

The president had previously said he would veto the giant defense bill, which passed through both chambers of Congress with veto-proof majorities. Trump’s move sets up a veto override vote in the House and Senate and if successful, would be the first veto override of Trump’s presidency.

The president tweeted his reason for the veto earlier this month, writing: "I hope House Republicans will vote against the very weak National Defense Authorization Act (NDAA), which I will VETO. Must include a termination of Section 230 (for National Security purposes), preserve our National Monuments, & allow for 5G & troop reductions in foreign lands!"

Trump objections to the Section 230 legal protections for Big Tech companies such as Facebook and Twitter, which he and Republicans claim are unfair to Republicans. He also opposes a provision that we re-name military bases named after Confederate war heroes.

--ABC News’ Katherine Faulders

Vice president-elect Kamala Harris lauded Miguel Cardona’s nomination to education secretary in remarks Wednesday, saying he “represents the very best of our nation.”

Harris also pledged that she and Biden would continue fighting for additional relief for schools.

“We need to get this virus under control and reopen our schools safely as the resident-elect always says, and that is why the president-elect and I are supporting funding for our education system in this recently-passed COVID-19 relief legislation,” she said. “And we will continue to fight for additional emergency relief for our educators and our schools.”

“And even as we do, we must also build a public education system that lifts up all Americans, regardless of race, background, or zip code,” Harris added.

Harris said that under Cardona’s leadership, “we will work together to put together an outstanding education system that will be within reach for everyone, breaking down barriers to equality, opening new paths to opportunity and helping to fulfill America's promise to all of our children.”

Biden’s education secretary pick, Miguel Cardona, also spoke at the event in Wilmington, Delaware, where the president-elect introduced him to the public on Wednesday.

“I know how challenging this year has been for students, for educators and for parents,” Cardona said. “I’ve lived those challenges alongside millions of American families. Not only in my role as state education commissioner, but as a public school parent.”

“For so many of our schools, far too many of our students, this unprecedented year has piled on crisis after crisis,” he added. “It's taken some of our most painful, longstanding disparities and wrenched them open even wider.”

Cardona spoke about his childhood growing up in public housing and his time attending public schools in Connecticut, saying this is where he was able to expand his horizons and become the first in his family to graduate college.

“I, being bilingual and bicultural, am as American as apple pie and rice and beans,” he said. “For me, education was the great equalizer. But for too many students, your zip code and your skin color remain the best predictor of the opportunities you'll have in your lifetime.”

“We must embrace the opportunity to reimagine education and build it back better,” he added.

Cardona said he is “grateful for the chance to take on this responsibility” as education secretary.

“I look forward to getting to work on behalf of America's children and the families and the communities and the nation they will grow up to inherit and lead,” Cardona said.

The president-elect and vice president-elect publicly introduced Miguel Cardona as their nominee for secretary of education at an event in Wilmington, Delaware, on Wednesday. Cardona is currently Connecticut's commissioner of education.

“Once again during this pandemic we’ve seen who our educators are -- they are selfless, they are dedicated and they are cut from a true cloth of character and commitment,” Biden said. “They represent one of the most critical professions in America and that’s not hyperbole, that’s a fact.”

“In this critical moment of our nation's history, it’s essential that there is an educator serving as secretary of education,” he added, pledging that Cardona will be ready “on day one.”

Biden also mentioned the historic nature of his Cabinet, saying, “already there are more people of color in this Cabinet than any Cabinet in the history of the United States.”

Biden pledged his team will open schools safely and that this will be a “national priority for the administration.”

The president-elect said that the next education secretary needs to be someone “who understands the need to prevent the pandemic from further exacerbating the inequities in our education system.” He noted how remote learning has been especially difficult for low-income communities.

Biden added that we need to make sure "every child in this nation has access to good education regardless of zip code."

“The secretary of education we nominate is Dr. Miguel Cardona, fourth-grade public school teacher, the youngest principal in the state of Connecticut, first official Latino to serve as the education commissioner," Biden said.

President-elect Joe Biden is expected to name Miguel Cardona, who currently serves as Connecticut's education commissioner, as his pick for secretary of education, sources familiar with the decision told ABC News on Tuesday.

Throughout his presidential campaign Biden pledged to select a schoolteacher to lead the department, and Cardona fulfills that pledge, having started his career nearly two decades ago as an elementary school teacher in Connecticut, serving 10 years as a school principal and eventually rising through the ranks to become the state's top education official last year.

"First thing, as president of United States -- not a joke -- first thing I will do is make sure that the secretary of education is not Betsy DeVos, [and that] it is a teacher. A teacher. Promise," Biden, who regularly criticized Education Secretary Betsy DeVos, said at a National Education Association forum in July of 2019.

Cardona's background and deep experience in the nation's education system presents a striking contrast with DeVos, a wealthy, long-time Republican donor and political activist who has drawn sustained ire from Democrats and teachers unions throughout her tenure.

Cardona, whose parents moved from Puerto Rico to Connecticut, would be the third Latino, and the first of Puerto Rican heritage, that Biden has named to serve in his Cabinet thus far, following Alejandro Mayorkas named to head the Department of Homeland Security and California Attorney General Xavier Beccera to head the Department of Health and Human Services.

A spokesman for the Biden transition did not respond to a request for comment from ABC News on Cardona's potential nomination.

-ABC News’ John Verhovek and Molly Nagle.