The Senate is set for a showdown at noon Tuesday that will likely see Betsy DeVos, President Trump's nominee for education secretary, confirmed by the slimmest of margins with the help of Vice President Mike Pence, who is expected to cast a tie-breaking vote.

DeVos, who has been uniformly opposed by Senate Democrats, is perhaps the most reviled pick among Trump's Cabinet and administration selections. A staunch supporter of school choice, DeVos faced contentious confirmation hearings and even saw two Republicans break ranks and oppose her nomination.

Last week, GOP Sens. Susan Collins of Maine and Lisa Murkowski of Alaska announced during speeches on the Senate floor that they would oppose DeVos, leaving Democrats one vote away from blocking her nomination altogether. The defections are forcing Pence to preside for the vote, which is believed to be the first time a sitting vice president will cast the deciding vote for a Cabinet nominee.

However, only hours before the vote, Democrats are not optimistic about winning over a third Republican.

"It's unlikely we're going to get that 51st vote but we're going to try until the very last minute," Sen. Chris Murphy, D-Conn., told CNN Tuesday morning.

DeVos' confirmation would be a severe blow to the teachers' unions, who have adamantly opposed her confirmation since Trump announced her nomination to the post in late November. Randi Weingarten, the president of the American Federation for Teachers, has labeled her the "the most ideological, anti-public education nominee" since the post became a Cabinet position four decades ago.

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Senators on both sides say their offices have received a severe spike in calls and emails from constituents, the majority of whom are calling on them to oppose DeVos. Members have asked constituents directly to stop calling their office and send emails as the phone lines have been jammed in recent days.

Senate Democrats have also held the floor for the past 30 hours and spoke out against a possible DeVos confirmation. It's likely all for naught.

"She seemed to not have any recognition of the federal law that protects students with disabilities in our schools," Murphy said, adding that DeVos has a "lack of compassion" for the shootings at Sandy Hook Elementary School and an "inability to understand" basic law to help vulnerable students.

A former chairwoman of the Michigan Republican Party, DeVos has been a longtime supporter of giving families vouchers to attend private schools, an advocate for charter schools, as well as an enemy of public schools, which Collins pointed to as a reason for her opposition to DeVos' nomination.

However, the White House has consistently stood behind her for the post. While making the Sunday show rounds over the weekend, Pence said it would be a "high honor" to cast the tie-breaking vote for her on Tuesday.

The Senate is expected to vote later in the week for Sen. Jeff Sessions, R-Ala., Trump's pick to serve as attorney general, who will be needed in the Senate Tuesday to help confirm DeVos.