Charter school advocate Betsy DeVos won confirmation as education secretary Tuesday by the slimmest of margins, pushed to approval only by the historic tie-breaking vote of U.S. Vice-President Mike Pence.

Two Republicans, Susan Collins of Maine and Lisa Murkowski of Alaska, joined Democrats in a marathon effort to derail the nomination of the wealthy Republican donor. The Senate historian said Pence's vote was the first by a vice-president to break a 50-50 tie on a cabinet nomination.

DeVos was formally sworn in to the position Tuesday evening.

Despite the win, DeVos emerged bruised from the highly divisive nomination fight. Opposed by half the Senate, she faced criticism, even ridicule for lack of experience and confusion during her confirmation hearing. At one point, she said some schools should have guns because of the threat of grizzly bears.

And there has been scathing opposition from teachers unions and civil rights activists over her support of charter schools and her conservative religious ideology.

In a tweet before the vote, U.S. President Donald Trump accused Democrats of seeking to torpedo education progress.

DeVos was sworn in hours after the Senate vote by Pence, who told the new cabinet member: "I wasn't just voting for you. Having seen your devotion to improving the quality of education for some of our most vulnerable children across the nation for so many years, I was also casting a vote for America's children."

"I can tell you, my vote for Betsy DeVos was the easiest vote I ever cast," Pence said.

She now takes the helm of a department charged with implementing laws affecting the nation's public schools. Her opponents noted that she has no experience running public schools, nor has she attended one or sent her children to one

She also will have to address several hot-button issues in higher education, such as rising tuition costs, growing student debt and the troubled for-profit colleges, many of which have closed down, leaving students with huge loans and without a good education or job prospects.

Close attention also will be paid to how DeVos deals with sexual assault and freedom of speech on campuses.

Ahead of Tuesday's vote, emotions ran high as constituents jammed senators' phone lines. Protesters gathered outside the Capitol, including one person in a grizzly bear costume to ridicule DeVos.

Democrats and labour unions vigorously fought the nomination, suggesting that DeVos would defund traditional public schools by diverting taxpayers' money to charter and private institutions. They cited her financial interest in organizations pushing for charter schools, though she has said she will divest those interests.

Collins and Murkowski said they feared her focus on charter schools will undermine remote public schools in their states.

"President Trump's swamp got a new billionaire today," the Democratic National Committee said in a statement. "Millions of teachers, parents and students could not have made their opposition to Betsy DeVos' confirmation any clearer — they do not want someone whose only education experience is dismantling public schools."

DeVos supporters, however, saw her confirmation as an occasion to breathe new life into a troubled American school system and a chance to shift power from Washington to the local level.

"She has been a leader in the movement for public charter schools — the most successful reform of public education during the last 30 years," said Senator Lamar Alexander, the chairman of the education committee. "And she has worked tirelessly to help low-income children have more choices of better schools."

DeVos has her work cut out for her.

"She will have to make it a priority to reach out to educators and education policy makers to reassure them that she is committed to working to improve education for all students including the vast majority who attend and will continue to attend traditional public schools," said Martin West, associate professor of education at Harvard University. "My view is that she is committed to doing that."

In addition to DeVos, Republicans hope to confirm a series of other divisive nominees this week: Alabama Republican Senator Jeff Sessions as attorney general, Republican Representative Tom Price of Georgia as health secretary and financier Steven Mnuchin as treasury secretary.