Mike Pence at the ready to vote for Kavanaugh if Republican senators fail to reach confirmation threshold

Republicans have little margin of error if they want to confirm Mr Kavanaugh to the US Supreme Court

Mr Pence is standing by to cast a decisive vote for Mr Kavanaugh if necessary (AP)

With a razor-thin margin of error, Vice President Mike Pence is standing by to vote in favour of Supreme Court nominee Brett Kavanaugh should Republicans be unable to corral 51 votes to confirm the judge outright.

Republicans control the Senate 51 to 49, making Mr Pence’s involvement a potential necessity if just one GOP senator decides to vote against Mr Kavanaugh’s nomination.

As it stands, three Republican senators have signalled they are on the fence about whether to elevate Mr Kavanaugh — Senators Lisa Murkowski, Susan Collins, and Jeff Flake. Red-state Democrat Joe Manchin also voted in favour of sending Kavanaugh to a final vote, and many think he's likely to vote in favour of the judge.

Tensions are high in Washington, where the Senate voted on Friday for cloture, a procedural hurdle that sets up a final confirmation vote for Saturday.

As the Senate considers what to do, protesters have swarmed the capitol, and hundreds of anti-Kavanaugh demonstrators have been detained by police. On Thursday, protesters filled the Hart Senate Office Building, urging senators to drop Mr Kavanaugh and look to another nominee.

Mr Kavanaugh’s confirmation was thrust into controversy after Dr Christine Blasey Ford, a California university professor, came forward with accusations that the nominee had sexually assaulted him while they were both teenagers more than 30 years ago. In her Senate testimony, Dr Ford said that Mr Kavanaugh had drunkenly assaulted her at a house party while they were in high school, groping her, attempting to remove her clothes, and holding her mouth shut so she could not scream.

She said that she is absolutely certain Mr Kavanaugh was the man who assaulted her. Mr Kavanaugh has denied all allegations of sexual misconduct that have been made against him — including those from his second accuser, Deborah Ramirez, who has alleged that Mr Kavanaugh forced her to touch his penis against her will during a party at Yale University, where they both attended.

Mr Flake, one of the potential swing votes in Mr Kavanaugh’s nomination, played an important role in forcing the Senate to follow up on those allegations. While he voted in favour of sending Mr Kavanaugh’s nomination to the full Senate from the Judiciary Committee, he also urged an FBI investigation into the allegations.

The FBI’s investigation concluded on Wednesday, and a report was sent to the White House and Senate. Senators reviewed those documents on Thursday, with Ms Collins and Mr Flake indicating they felt the investigation was adequately thorough. Democrats, meanwhile, cast the investigation as a sham. Some called it a cover up.