Judge Brett M. Kavanaugh cleared a major hurdle on Friday morning in his quest for the Supreme Court, as the Senate voted narrowly to cut off debate on his nomination and move to a final vote as early as Saturday, but one Republican senator left open the possibility that she could still vote no.

The 51-49 vote is the next-to-last step in the most tumultuous Supreme Court confirmation process in decades.

Senator Susan Collins, Republican of Maine, said her vote to move the confirmation forward did not signal how she will vote in the end. Instead, she will announce her position on Judge Kavanaugh later.

Senator Joe Manchin III, Democrat of West Virginia, also voted yes, freeing Vice- President Mike Pence from a tie-breaking vote on the nomination after Senator Lisa Murkowski, Republican of Alaska, voted no.

Senator Jeff Flake, Republican of Arizona, told reporters he will vote for Judge Kavanaugh this weekend “unless something big changes”. Manchin gave no indication of whether his procedural vote reflected his final position. A spokesman for Manchin said he would not make any more comments on Friday.

Murkowski, however, appears set. She said she wrestled deeply with the decision — which she did not make until she walked into the Senate chamber on Friday morning. But she would not change her vote.

“I believe we’re dealing with issues right now that are bigger than the nominee, and how we ensure fairness and how our legislative and judicial branch can continue to be respected,” she said, choosing her words carefully, her voice filled with emotion.

“This is what I have been wrestling with, and so I made the — took the very difficult vote that I did,” she said. “I believe Brett Kavanaugh’s a good man. It just may be that in my view he’s not the right man for the court at this time.”

For Judge Kavanaugh, and the country, the stakes are huge: If confirmed, President Trump’s second Supreme Court nominee will replace the high court’s swing vote — as cast by retired Justice Anthony M. Kennedy — with a committed conservative, shifting the ideological balance on the court towards the Right for generations.

Friday’s vote ushers in 30 hours of debate before the Senate takes its final vote on Judge Kavanaugh. It came as senators were still absorbing the results of a confidential FBI inquiry into allegations of sexual assault against the judge — claims that have torn apart the Senate and divided the nation.

In divergent and often bitter remarks before the Friday morning vote, senior senators delivered closing arguments that demonstrated how deeply the nomination has split the Senate. Senator Charles E. Grassley, Judiciary Committee chairman, accused Democrats of waging a scorched-earth campaign to destroy Judge Kavanaugh — “the most qualified nominee in our history” — before he could be confirmed.