(CNN) -- Republican Sens. Susan Collins of Maine and Sen. Lisa Murkowski of Alaska both said Wednesday they would not vote to support Betsy DeVos, President Donald Trump's choice for education secretary. The two women are the first sitting Republican senators to publicly say they wouldn't back one of Trump's Cabinet nominees.
"I simply cannot support her confirmation," Collins said on the Senate floor.
The stunning decision from a pair of veteran Republican lawmakers puts DeVos in a tenuous position as her final vote before the Senate nears.
It also puts the onus on Senate Republican leadership and the White House to keep every other Republican senator on board with DeVos. If Republicans can maintain 50 votes in support of DeVos, then Vice President Mike Pence would become the tie-breaking vote for DeVos.
Questions emerged Tuesday after reports that DeVos appeared to have lifted key sections of her written answers from other authors, spurring the lead Democrat opposing her to say she was reviewing the potential plagiarism.
DeVos has been a major player in the conservative education reform movement for decades --- but more often behind the scenes as a major political donor in state-level races than in the public eye.
DeVos' rocky performance at her confirmation hearing last month --- which ended in part by her being lampooned on social media for suggesting schools keep guns for grizzly bears --- led to a flood of emails and calls from opponent