(CBS News) Chief Justice John Roberts initially sided with the Supreme Court's four conservative justices to strike down the heart of President Obama's health care reform law, the Affordable Care Act, but later changed his position and formed an alliance with liberals to uphold the bulk of the law, according to two sources with specific knowledge of the deliberations.
Roberts then withstood a month-long, desperate campaign to bring him back to his original position, the sources said. Ironically, Justice Anthony Kennedy - believed by many conservatives to be the justice most likely to defect and vote for the law - led the effort to try to bring Roberts back to the fold.
"He was relentless," one source said of Kennedy's efforts. "He was very engaged in this."
But this time, Roberts held firm. And so the conservatives handed him their own message which, as one justice put it, essentially translated into, "You're on your own."
The conservatives refused to join any aspect of his opinion, including sections with which they agreed, such as his analysis imposing limits on Congress' power under the Commerce Clause, the sources said.
Instead, the four joined forces and crafted a highly unusual, unsigned joint dissent. They deliberately ignored Roberts' decision, the sources said, as if they were no longer even willing to engage with him in debate.
The inner-workings of the Supreme Court are almost impossible to penetrate. The court's private conferences, when the justices discuss cases and cast their initial votes, include only the nine members - no law clerks or secretaries are permitted. The justices are notoriously close-lipped, and their law clerks must agree to keep matters completely confidential.
But in this closely-watched case, word of Roberts' unusual shift has spread widely within the court, and is known among law clerks, chambers' aides and secretaries. It also has stirred the ire of the conservative justices, who believed Roberts was standing with them.
After the historic oral arguments in March, the two knowledgeable sources said, Roberts and the four conservatives were poised to strike down at least the individual mandate. There were other issues being argued - severability and the Medicaid extension - but the mandate was the ballgame.
It required individuals to buy insurance or pay a penalty. Congress had never before in the history of the nation ordered Americans to buy a product from a private company as part of its broad powers to regulate commerce. Opponents argued that the law exceeded Congress' power under the Constitution, and an Atlanta-based federal appeals court agreed.
The Atlanta-based federal appeals court said Congress didn't have that kind of expansive power, and it struck down the mandate as unconstitutional.
On this point - Congress' commerce power - Roberts agreed. In the court's private conference immediately after the arguments, he was aligned with the four conservatives to strike down the mandate.
Roberts was less clear on whether that also meant the rest of the law must fall, the source said. The other four conservatives believed that the mandate could not be lopped off from the rest of the law and that, since one key part was unconstitutional, the entire law must be struck down.
Because Roberts was the most senior justice in the majority to strike down the mandate, he got to choose which justice would write the court's historic decision. He kept it for himself.
Over the next six weeks, as Roberts began to craft the decision striking down the mandate, the external pressure began to grow. Roberts almost certainly was aware of it.