Aaron P. Bernstein/Getty Images

Senate Democrats plan to hold the floor for the next 24 hours to protest the nomination of Betsy DeVos, President Trump's pick for education secretary. At the start of the all-night debate Monday, Senate Minority Leader Chuck Schumer (D-N.Y.) declared DeVos the "least qualified nominee in a historically unqualified Cabinet," and Sen. Patty Murray (D-Wash.) promised Democrats will do "everything we can to persuade just one more Republican to join us."

Already, Republican Sens. Susan Collins (Maine) and Lisa Murkowswki (Alaska) have said they will oppose DeVos, which may make it necessary for Vice President Mike Pence to step in to cast a tie-breaking vote in DeVos' favor. Politico noted if that were to happen, it would mark "the first time a vice president has needed to cast the tie-breaking vote for a Cabinet secretary." If another Republican decides to vote against DeVos, however, she will not be confirmed.

The Democrats' marathon session is slated to last until noon Tuesday, at which point the Senate will hold a final vote on DeVos' confirmation.