Supreme Court Justice Brett Kavanaugh reportedly was among the top five choices that former Justice Anthony Kennedy recommended then-candidate Donald Trump nominate during the 2016 campaign.

That was just one of the many revelations contained in a new book by Federalist editor and Fox News contributor Mollie Hemingway and Judicial Crisis Network chief counsel Carrie Severino. Hemingway and Severino write that Kavanaugh was one of Kennedy's top recommendations to the Trump campaign.

“While Kennedy called his other clerks good or excellent, he tended to describe Kavanaugh as brilliant,” the book claims.

In writing "Justice on Trial: The Kavanaugh Confirmation and the Future of the Supreme Court," the authors interviewed more than 100 sources, including high-ranking officials in the White House and Justice Department.

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Kavanaugh, who previously served as Kennedy's clerk, was initially bypassed when the administration nominated Supreme Court Justice Neil Gorsuch to replace former Justice Antonin Scalia. He was later nominated to replace Kennedy himself.

According to the book, Kavanaugh wasn't even on Trump's initial list of prospective Supreme Court nominees. Kavanaugh, a former adviser to President George W. Bush, "was not what the anti-establishment Trump was looking for," the book claims.

Kavanaugh's strength, the authors said, came from his lengthy record as a judge and his broad network of support. "Kavanaugh had a broad network of friends and allies -- from federal judges to conservative media stars to his family dry cleaner -- who could vouch for his ability and character and thought he should not just be on the list but at the top" (emphasis authors').

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News of Kennedy's input provoked criticism from the group Fix the Court.

"It is a clear violation of judicial ethics for a sitting Supreme Court justice to advise a presidential campaign, as a new book reports Justice Kennedy did in 2016… Instead of engaging, Kennedy should have referred campaign staff to any number of publicly available compilations of potential nominees in a Republican administration," Fix the Court director Gabe Roth said in a statement.

Fox News' Bill Mears contributed to this report.