A new book on Supreme Court Chief Justice John Roberts offers new details of his negotiation with liberal justices Elena Kagan and Stephen Breyer to save ObamaCare ahead of the court's landmark ruling in 2012, according to excerpts released on CNN.

In Joan Biskupic's "The Chief: The Life and Turbulent Times of Chief Justice John Roberts," which is scheduled for release next Tuesday, she writes that Roberts originally opposed upholding the Affordable Care Act's individual mandate that required people to buy insurance, and cast his initial vote to strike it down, but he did join the liberal justices in voting to uphold Medicaid expansion, according to the book. He later shifted on both issues.

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"The chief justice then turned to Breyer and Kagan, the liberals most likely to work with him on contentious issues, to see if they could find common ground," Biskupic writes.

"If there was a chance that Roberts would cast the critical vote to uphold the central plank of Obamacare — and negotiations in May were such that they still considered that a shaky proposition — they were willing to meet him partway."

Roberts siding with the court's more liberal justices brought him much criticism from the right. He was slammed in opinion pieces, and future President TrumpDonald John TrumpLiz Cheney: 'Send her back' chant 'inappropriate' but not about race, gender Booker: Trump is 'worse than a racist' Top Democrat insists country hasn't moved on from Mueller MORE condemned him on Twitter.

Roberts's reversal on the Medicaid decision allowed many Republican-controlled states to block the expansion of the program.