Josh Douglas, another United Kingdom law professor who signed the letter, said in an email to WKYT that Kavanaugh's performance was "disturbing".
Their support makes Saturday's vote to confirm Kavanaugh an apparent formality after a battle that riveted the nation for almost a month.
Her vote is disappointing enough, but her speech was a giant middle finger to all survivors of sexual assault.
Democrats railed against the nomination in Senate floor speeches Friday night and Saturday morning, and protests opposing Kavanaugh are expected throughout the day on Saturday.
Manchin voted yes, and he, Collins and Flake said later that they would also back his confirmation Saturday, when Majority Leader Mitch McConnell has scheduled a final vote on Kavanaugh's nomination to replace retired Justice Anthony Kennedy.
Flake was joined in his vote for cloture by every other Senate Republican except Lisa Murkowski (R-AK). She said, however, that she sets a high bar for nominees to win confirmation and talked about the importance of selecting judges who will act at all times in a manner that promotes "public confidence" in the judiciary.
Both Kavanaugh and the first accuser made a dramatic testimony before the Senate Judiciary Committee which was watched live by millions of people across the world. Rob Portman of OH came over to Murkowski and took her hand, shaking it. Texas Sen.
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Senators are expected to vote on Brett Kavanaugh's nomination to the Supreme Court starting around 5 p.m. ET Saturday.
Brett Kavanaugh's elevation to the US Supreme Court is all but assured.
With the confirmed support of him and Collins, the likely final Senate vote is 51-49. She also said that while she believed Christine Blasey Ford was a victim of trauma, she cast doubt on Ford's story.
"We will be ill-served in the long run if we abandon the presumption of innocence and fairness, tempting though it may be", Collins said in remarks that stretched for more than 40 minutes but addressed the sexual-abuse allegations only near the end. The moderate Republican previously expressed support for the additional background check the Federal Bureau of Investigation concluded a day earlier into allegations of sexual misconduct against Kavanaugh.