A new book helps back up what conservatives have long suspected: Chief Justice John Roberts treated the Supreme Court as a legislative body in his 2012 effort to save Obamacare.

In her book The Chief, legal reporter Joan Biskupic provides an account of Roberts' deliberations in the 2012 case challenging the constitutionality of Obamacare's individual mandate. All normal caveats should apply, as the Supreme Court is a famously secretive institution that closely guards private negotiations. But the account she provides does jibe with what conservatives have been been complaining about for the past seven years.

Roberts went back and forth in his deliberations, effectively deciding first that he wanted to at least partially overturn Obamacare while saving most of it, and then he spent the rest of the time negotiating with other justices to reverse engineer a decision that enabled him to do that.

In the first vote following the oral arguments, Biskupic reveals, Roberts not only voted to strike down the individual mandate, but also to uphold the law's Medicaid expansion, the exact opposite of the ultimate ruling.

"He acknowledged being torn between his heart and his head, as he put it, and expressed some hesitancy to strike down a law intended to solve the nation's health insurance crisis," according to the book.

In reality, such emotional or policy considerations should be irrelevant to whether a given piece of legislation passes legal muster.

The book goes on to explain that, as the process moved forward, "Roberts wanted to craft a compromise decision that could validate a portion of the [Affordable Care Act]. But his four fellow conservatives believed that if the individual mandate was going down, it would take the whole law with it."

In other words, Roberts agreed that the individual mandate was unconstitutional, but was concerned about scrapping the whole law, so he searched for a "compromise."

"Although Roberts remained firm in his belief that the individual mandate exceeded Congress's commerce power, he did not want the entire law to fall," Biskupic writes.

What he started to gravitate toward was the government's fallback argument, that the mandate could be legally justified as a tax. He was undeterred by the fact that the mandate was not described as a tax in the legislation, did not appear in the revenue section of the bill, and was used to coerce individuals into doing something Congress, according to Roberts, did not otherwise have the power to do.

And so, "He continued to try and negotiate with [Anthony] Kennedy, but he now also turned to [Stephen] Breyer and [Elena] Kagan, the liberal justices most likely to work with him on contentious issues, to find a common ground." The book goes on to explain that, "Breyer and Kagan, who were conferring with Roberts, had voted in the justices' private conference to uphold the new Medicaid requirement to help the poor, and their votes had been unequivocal. But they were aware that Roberts was now making a concession on the individual mandate and they were open to compromising."

In his confirmation hearing, Roberts famously described his job as being an umpire rather than a player. He promised, "I will remember that it’s my job to call balls and strikes, and not to pitch or bat."

Nonetheless, when it came to Obamacare, Roberts had a desired outcome in mind, and negotiated as if he were chairman of a congressional committee tasked with writing the bill, rather than as a chief justice dispassionately judging its constitutionality.