Story highlights Trump's pick for education secretary has run into strong opposition

Vice President Mike Pence will likely have to be called on as the tie-breaker

Washington (CNN) Vice President Mike Pence cast a historic tie-breaking vote Tuesday to confirm Betsy DeVos as the next education secretary after the Senate was evenly divided over the controversial pick.

The 51-50 vote ends Trump's toughest confirmation battle yet. Senate Democrats debated through the night and into Tuesday morning in a last-ditch attempt to derail DeVos, buoyed by support from Republican Sens. Lisa Murkowski of Alaska and Susan Collins of Maine.

DeVos was sworn into office shortly after 6 p.m. ET. Pence administered the oath of office and said his confirmation vote earlier in the day was "the easiest vote I ever cast."

Throughout the fight, Democrats argued they needed "Just one more!" to lure away another Republican vote. But Senate Republican leaders succeeded in delivering a victory to Trump in a confirmation fight that very few expected to become as tough as it did.

DeVos' poor performance in her confirmation hearing -- punctuated by her suggestion that a school in Wyoming might want to have guns on premises to protect against grizzly bears -- contributed to roaring anger among public school supporters and teachers unions. Even before her hearing, critics pointed to DeVos's lack of experience with public schools and her bankrolling of efforts like school vouchers that could take money from public institutions.